the PDL::Primitive manpage
 NAME
 DESCRIPTION
 SYNOPSIS
 FUNCTIONS
 inner
 outer
 x
 matmult
 innerwt
 inner2
 inner2d
 inner2t
 crossp
 norm
 indadd
 conv1d
 in
 uniq
 uniqind
 uniqvec
 hclip
 lclip
 clip
 clip
 wtstat
 statsover
 stats
 histogram
 whistogram
 histogram2d
 whistogram2d
 fibonacci
 append
 glue
 axisvalues
 random
 randsym
 grandom
 vsearch
 vsearch_sample
 vsearch_insert_leftmost
 vsearch_insert_rightmost
 vsearch_match
 vsearch_bin_inclusive
 vsearch_bin_exclusive
 interpolate
 interpol
 interpND
 one2nd
 which
 which_both
 where
 whereND
 whichND
 setops
 intersect
 AUTHOR
NAME
PDL::Primitive  primitive operations for pdl
DESCRIPTION
This module provides some primitive and useful functions defined using PDL::PP and able to use the new indexing tricks.
See PDL::Indexing for how to use indices creatively. For explanation of the signature format, see PDL::PP.
SYNOPSIS
# Pulls in PDL::Primitive, among other modules.
use PDL;
# Only pull in PDL::Primitive:
use PDL::Primitive;
FUNCTIONS
inner
Signature: (a(n); b(n); [o]c())
Inner product over one dimension
c = sum_i a_i * b_i
If a() * b()
contains only bad data, c()
is set bad. Otherwise c()
will have its bad flag cleared, as it will not contain any bad values.
outer
Signature: (a(n); b(m); [o]c(n,m))
outer product over one dimension
Naturally, it is possible to achieve the effects of outer product simply by threading over the "*
" operator but this function is provided for convenience.
outer processes bad values. It will set the badvalue flag of all output piddles if the flag is set for any of the input piddles.
x
Signature: (a(i,z), b(x,i),[o]c(x,z))
Matrix multiplication
PDL overloads the x
operator (normally the repeat operator) for matrix multiplication. The number of columns (size of the 0 dimension) in the lefthand argument must normally equal the number of rows (size of the 1 dimension) in the righthand argument.
Row vectors are represented as (N x 1) twodimensional PDLs, or you may be sloppy and use a onedimensional PDL. Column vectors are represented as (1 x N) twodimensional PDLs.
Threading occurs in the usual way, but as both the 0 and 1 dimension (if present) are included in the operation, you must be sure that you don't try to thread over either of those dims.
EXAMPLES
Here are some simple ways to define vectors and matrices:
pdl> $r = pdl(1,2); # A row vector
pdl> $c = pdl([[3],[4]]); # A column vector
pdl> $c = pdl(3,4)>(*1); # A column vector, using NiceSlice
pdl> $m = pdl([[1,2],[3,4]]); # A 2x2 matrix
Now that we have a few objects prepared, here is how to matrixmultiply them:
pdl> print $r x $m # row x matrix = row
[
[ 7 10]
]
pdl> print $m x $r # matrix x row = ERROR
PDL: Dim mismatch in matmult of [2x2] x [2x1]: 2 != 1
pdl> print $m x $c # matrix x column = column
[
[ 5]
[11]
]
pdl> print $m x 2 # Trivial case: scalar mult.
[
[2 4]
[6 8]
]
pdl> print $r x $c # row x column = scalar
[
[11]
]
pdl> print $c x $r # column x row = matrix
[
[3 6]
[4 8]
]
INTERNALS
The mechanics of the multiplication are carried out by the matmult method.
matmult
Signature: (a(t,h); b(w,t); [o]c(w,h))
Matrix multiplication
Notionally, matrix multiplication $a x $b is equivalent to the threading expression
$a>dummy(1)>inner($b>xchg(0,1)>dummy(2),$c);
but for large matrices that breaks CPU cache and is slow. Instead, matmult calculates its result in 32x32x32 tiles, to keep the memory footprint within cache as long as possible on most modern CPUs.
For usage, see x, a description of the overloaded 'x' operator
matmult ignores the badvalue flag of the input piddles. It will set the badvalue flag of all output piddles if the flag is set for any of the input piddles.
innerwt
Signature: (a(n); b(n); c(n); [o]d())
Weighted (i.e. triple) inner product
d = sum_i a(i) b(i) c(i)
innerwt processes bad values. It will set the badvalue flag of all output piddles if the flag is set for any of the input piddles.
inner2
Signature: (a(n); b(n,m); c(m); [o]d())
Inner product of two vectors and a matrix
d = sum_ij a(i) b(i,j) c(j)
Note that you should probably not thread over a
and c
since that would be very wasteful. Instead, you should use a temporary for b*c
.
inner2 processes bad values. It will set the badvalue flag of all output piddles if the flag is set for any of the input piddles.
inner2d
Signature: (a(n,m); b(n,m); [o]c())
Inner product over 2 dimensions.
Equivalent to
$c = inner($a>clump(2), $b>clump(2))
inner2d processes bad values. It will set the badvalue flag of all output piddles if the flag is set for any of the input piddles.
inner2t
Signature: (a(j,n); b(n,m); c(m,k); [t]tmp(n,k); [o]d(j,k)))
Efficient Triple matrix product a*b*c
Efficiency comes from by using the temporary tmp
. This operation only scales as N**3
whereas threading using inner2 would scale as N**4
.
The reason for having this routine is that you do not need to have the same threaddimensions for tmp
as for the other arguments, which in case of large numbers of matrices makes this much more memoryefficient.
It is hoped that things like this could be taken care of as a kind of closures at some point.
inner2t processes bad values. It will set the badvalue flag of all output piddles if the flag is set for any of the input piddles.
crossp
Signature: (a(tri=3); b(tri); [o] c(tri))
Cross product of two 3D vectors
After
$c = crossp $a, $b
the inner product $c*$a
and $c*$b
will be zero, i.e. $c
is orthogonal to $a
and $b
crossp does not process bad values. It will set the badvalue flag of all output piddles if the flag is set for any of the input piddles.
norm
Signature: (vec(n); [o] norm(n))
Normalises a vector to unit Euclidean length
norm processes bad values. It will set the badvalue flag of all output piddles if the flag is set for any of the input piddles.
indadd
Signature: (a(); indx ind(); [o] sum(m))
Threaded Index Add: Add a
to the ind
element of sum
, i.e:
sum(ind) += a
Simple Example:
$a = 2;
$ind = 3;
$sum = zeroes(10);
indadd($a,$ind, $sum);
print $sum
#Result: ( 2 added to element 3 of $sum)
# [0 0 0 2 0 0 0 0 0 0]
Threaded Example:
$a = pdl( 1,2,3);
$ind = pdl( 1,4,6);
$sum = zeroes(10);
indadd($a,$ind, $sum);
print $sum."\n";
#Result: ( 1, 2, and 3 added to elements 1,4,6 $sum)
# [0 1 0 0 2 0 3 0 0 0]
The routine barfs if any of the indices are bad.
conv1d
Signature: (a(m); kern(p); [o]b(m); int reflect)
1D convolution along first dimension
The mth element of the discrete convolution of an input piddle $a
of size $M
, and a kernel piddle $kern
of size $P
, is calculated as
n = ($P1)/2
====
\
($a conv1d $kern)[m] = > $a_ext[m  n] * $kern[n]
/
====
n = ($P1)/2
where $a_ext
is either the periodic (or reflected) extension of $a
so it is equal to $a
on 0..$M1
and equal to the corresponding periodic/reflected image of $a
outside that range.
$con = conv1d sequence(10), pdl(1,0,1);
$con = conv1d sequence(10), pdl(1,0,1), {Boundary => 'reflect'};
By default, periodic boundary conditions are assumed (i.e. wrap around). Alternatively, you can request reflective boundary conditions using the Boundary
option:
{Boundary => 'reflect'} # case in 'reflect' doesn't matter
The convolution is performed along the first dimension. To apply it across another dimension use the slicing routines, e.g.
$b = $a>mv(2,0)>conv1d($kernel)>mv(0,2); # along third dim
This function is useful for threaded filtering of 1D signals.
Compare also conv2d, convolve, fftconvolve, fftwconv, rfftwconv
WARNING: conv1d
processes bad values in its inputs as the numeric value of $pdl>badvalue
so it is not recommended for processing pdls with bad values in them unless special care is taken.
conv1d ignores the badvalue flag of the input piddles. It will set the badvalue flag of all output piddles if the flag is set for any of the input piddles.
in
Signature: (a(); b(n); [o] c())
test if a is in the set of values b
$goodmsk = $labels>in($goodlabels);
print pdl(3,1,4,6,2)>in(pdl(2,3,3));
[1 0 0 0 1]
in
is akin to the is an element of of set theory. In priciple, PDL threading could be used to achieve its functionality by using a construct like
$msk = ($labels>dummy(0) == $goodlabels)>orover;
However, in
doesn't create a (potentially large) intermediate and is generally faster.
in does not process bad values. It will set the badvalue flag of all output piddles if the flag is set for any of the input piddles.
uniq
return all unique elements of a piddle
The unique elements are returned in ascending order.
PDL> p pdl(2,2,2,4,0,1,6,6)>uniq
[1 0 2 4 6] # 0 is returned 2nd (sorted order)
PDL> p pdl(2,2,2,4,nan,1,6,6)>uniq
[1 2 4 6 nan] # NaN value is returned at end
Note: The returned pdl is 1D; any structure of the input piddle is lost. NaN
values are never compare equal to any other values, even themselves. As a result, they are always unique. uniq
returns the NaN values at the end of the result piddle. This follows the Matlab usage.
See uniqind if you need the indices of the unique elements rather than the values.
Bad values are not considered unique by uniq and are ignored.
$a=sequence(10);
$a=$a>setbadif($a%3);
print $a>uniq;
[0 3 6 9]
uniqind
Return the indices of all unique elements of a piddle The order is in the order of the values to be consistent with uniq. NaN
values never compare equal with any other value and so are always unique. This follows the Matlab usage.
PDL> p pdl(2,2,2,4,0,1,6,6)>uniqind
[5 4 1 3 6] # the 0 at index 4 is returned 2nd, but...
PDL> p pdl(2,2,2,4,nan,1,6,6)>uniqind
[5 1 3 6 4] # ...the NaN at index 4 is returned at end
Note: The returned pdl is 1D; any structure of the input piddle is lost.
See uniq if you want the unique values instead of the indices.
Bad values are not considered unique by uniqind and are ignored.
uniqvec
Return all unique vectors out of a collection
NOTE: If any vectors in the input piddle have NaN values
they are returned at the end of the nonNaN ones. This is
because, by definition, NaN values never compare equal with
any other value.
NOTE: The current implementation does not sort the vectors
containing NaN values.
The unique vectors are returned in lexicographically sorted ascending order. The 0th dimension of the input PDL is treated as a dimensional index within each vector, and the 1st and any higher dimensions are taken to run across vectors. The return value is always 2D; any structure of the input PDL (beyond using the 0th dimension for vector index) is lost.
See also uniq for a uniqe list of scalars; and qsortvec for sorting a list of vectors lexicographcally.
If a vector contains all bad values, it is ignored as in uniq. If some of the values are good, it is treated as a normal vector. For example, [1 2 BAD] and [BAD 2 3] could be returned, but [BAD BAD BAD] could not. Vectors containing BAD values will be returned after any nonNaN and nonBAD containing vectors, followed by the NaN vectors.
hclip
Signature: (a(); b(); [o] c())
clip (threshold) $a
by $b
($b
is upper bound)
hclip processes bad values. It will set the badvalue flag of all output piddles if the flag is set for any of the input piddles.
lclip
Signature: (a(); b(); [o] c())
clip (threshold) $a
by $b
($b
is lower bound)
lclip processes bad values. It will set the badvalue flag of all output piddles if the flag is set for any of the input piddles.
clip
Clip (threshold) a piddle by (optional) upper or lower bounds.
$b = $a>clip(0,3);
$c = $a>clip(undef, $x);
clip handles bad values since it is just a wrapper around hclip and lclip.
clip
Signature: (a(); l(); h(); [o] c())
info not available
clip processes bad values. It will set the badvalue flag of all output piddles if the flag is set for any of the input piddles.
wtstat
Signature: (a(n); wt(n); avg(); [o]b(); int deg)
Weighted statistical moment of given degree
This calculates a weighted statistic over the vector a
. The formula is
b() = (sum_i wt_i * (a_i ** degree  avg)) / (sum_i wt_i)
Bad values are ignored in any calculation; $b
will only have its bad flag set if the output contains any bad data.
statsover
Signature: (a(n); w(n); float+ [o]avg(); float+ [o]prms(); int+ [o]median(); int+ [o]min(); int+ [o]max(); float+ [o]adev(); float+ [o]rms())
Calculate useful statistics over a dimension of a piddle
($mean,$prms,$median,$min,$max,$adev,$rms) = statsover($piddle, $weights);
This utility function calculates various useful quantities of a piddle. These are:
the mean:
MEAN = sum (x)/ N
with
N
being the number of elements in xthe population RMS deviation from the mean:
PRMS = sqrt( sum( (xmean(x))^2 )/(N1)
The population deviation is the bestestimate of the deviation of the population from which a sample is drawn.
the median
The median is the 50th percentile data value. Median is found by medover, so WEIGHTING IS IGNORED FOR THE MEDIAN CALCULATION.
the minimum
the maximum
the average absolute deviation:
AADEV = sum( abs(xmean(x)) )/N
RMS deviation from the mean:
RMS = sqrt(sum( (xmean(x))^2 )/N)
(also known as the rootmeansquare deviation, or the square root of the variance)
This operator is a projection operator so the calculation will take place over the final dimension. Thus if the input is Ndimensional each returned value will be N1 dimensional, to calculate the statistics for the entire piddle either use clump(1)
directly on the piddle or call stats
.
Bad values are simply ignored in the calculation, effectively reducing the sample size. If all data are bad then the output data are marked bad.
stats
Calculates useful statistics on a piddle
($mean,$prms,$median,$min,$max,$adev,$rms) = stats($piddle,[$weights]);
This utility calculates all the most useful quantities in one call. It works the same way as "statsover", except that the quantities are calculated considering the entire input PDL as a single sample, rather than as a collection of rows. See "statsover" for definitions of the returned quantities.
Bad values are handled; if all input values are bad, then all of the output values are flagged bad.
histogram
Signature: (in(n); int+[o] hist(m); double step; double min; int msize => m)
Calculates a histogram for given stepsize and minimum.
$h = histogram($data, $step, $min, $numbins);
$hist = zeroes $numbins; # Put histogram in existing piddle.
histogram($data, $hist, $step, $min, $numbins);
The histogram will contain $numbins
bins starting from $min
, each $step
wide. The value in each bin is the number of values in $data
that lie within the bin limits.
Data below the lower limit is put in the first bin, and data above the upper limit is put in the last bin.
The output is reset in a different threadloop so that you can take a histogram of $a(10,12)
into $b(15)
and get the result you want.
For a higherlevel interface, see hist.
pdl> p histogram(pdl(1,1,2),1,0,3)
[0 2 1]
histogram processes bad values. It will set the badvalue flag of all output piddles if the flag is set for any of the input piddles.
whistogram
Signature: (in(n); float+ wt(n);float+[o] hist(m); double step; double min; int msize => m)
Calculates a histogram from weighted data for given stepsize and minimum.
$h = whistogram($data, $weights, $step, $min, $numbins);
$hist = zeroes $numbins; # Put histogram in existing piddle.
whistogram($data, $weights, $hist, $step, $min, $numbins);
The histogram will contain $numbins
bins starting from $min
, each $step
wide. The value in each bin is the sum of the values in $weights
that correspond to values in $data
that lie within the bin limits.
Data below the lower limit is put in the first bin, and data above the upper limit is put in the last bin.
The output is reset in a different threadloop so that you can take a histogram of $a(10,12)
into $b(15)
and get the result you want.
pdl> p whistogram(pdl(1,1,2), pdl(0.1,0.1,0.5), 1, 0, 4)
[0 0.2 0.5 0]
whistogram processes bad values. It will set the badvalue flag of all output piddles if the flag is set for any of the input piddles.
histogram2d
Signature: (ina(n); inb(n); int+[o] hist(ma,mb); double stepa; double mina; int masize => ma;
double stepb; double minb; int mbsize => mb;)
Calculates a 2d histogram.
$h = histogram2d($datax, $datay, $stepx, $minx,
$nbinx, $stepy, $miny, $nbiny);
$hist = zeroes $nbinx, $nbiny; # Put histogram in existing piddle.
histogram2d($datax, $datay, $hist, $stepx, $minx,
$nbinx, $stepy, $miny, $nbiny);
The histogram will contain $nbinx
x $nbiny
bins, with the lower limits of the first one at ($minx, $miny)
, and with bin size ($stepx, $stepy)
. The value in each bin is the number of values in $datax
and $datay
that lie within the bin limits.
Data below the lower limit is put in the first bin, and data above the upper limit is put in the last bin.
pdl> p histogram2d(pdl(1,1,1,2,2),pdl(2,1,1,1,1),1,0,3,1,0,3)
[
[0 0 0]
[0 2 2]
[0 1 0]
]
histogram2d processes bad values. It will set the badvalue flag of all output piddles if the flag is set for any of the input piddles.
whistogram2d
Signature: (ina(n); inb(n); float+ wt(n);float+[o] hist(ma,mb); double stepa; double mina; int masize => ma;
double stepb; double minb; int mbsize => mb;)
Calculates a 2d histogram from weighted data.
$h = whistogram2d($datax, $datay, $weights,
$stepx, $minx, $nbinx, $stepy, $miny, $nbiny);
$hist = zeroes $nbinx, $nbiny; # Put histogram in existing piddle.
whistogram2d($datax, $datay, $weights, $hist,
$stepx, $minx, $nbinx, $stepy, $miny, $nbiny);
The histogram will contain $nbinx
x $nbiny
bins, with the lower limits of the first one at ($minx, $miny)
, and with bin size ($stepx, $stepy)
. The value in each bin is the sum of the values in $weights
that correspond to values in $datax
and $datay
that lie within the bin limits.
Data below the lower limit is put in the first bin, and data above the upper limit is put in the last bin.
pdl> p whistogram2d(pdl(1,1,1,2,2),pdl(2,1,1,1,1),pdl(0.1,0.2,0.3,0.4,0.5),1,0,3,1,0,3)
[
[ 0 0 0]
[ 0 0.5 0.9]
[ 0 0.1 0]
]
whistogram2d processes bad values. It will set the badvalue flag of all output piddles if the flag is set for any of the input piddles.
fibonacci
Signature: ([o]x(n))
Constructor  a vector with Fibonacci's sequence
fibonacci does not process bad values. It will set the badvalue flag of all output piddles if the flag is set for any of the input piddles.
append
Signature: (a(n); b(m); [o] c(mn))
append two or more piddles by concatenating along their first dimensions
$a = ones(2,4,7);
$b = sequence 5;
$c = $a>append($b); # size of $c is now (7,4,7) (a jumbopiddle ;)
append
appends two piddles along their first dims. Rest of the dimensions must be compatible in the threading sense. Resulting size of first dim is the sum of the sizes of the first dims of the two argument piddles  ie n + m
.
Similar functions include glue (below) and cat.
append does not process bad values. It will set the badvalue flag of all output piddles if the flag is set for any of the input piddles.
glue
$c = $a>glue(<dim>,$b,...)
Glue two or more PDLs together along an arbitrary dimension (ND append).
Sticks $a, $b, and all following arguments together along the specified dimension. All other dimensions must be compatible in the threading sense.
Glue is permissive, in the sense that every PDL is treated as having an infinite number of trivial dimensions of order 1  so $a>glue(3,$b)
works, even if $a and $b are only one dimensional.
If one of the PDLs has no elements, it is ignored. Likewise, if one of them is actually the undefined value, it is treated as if it had no elements.
If the first parameter is a defined perl scalar rather than a pdl, then it is taken as a dimension along which to glue everything else, so you can say $cube = PDL::glue(3,@image_list);
if you like.
glue
is implemented in pdl, using a combination of xchg and append. It should probably be updated (one day) to a pure PP function.
Similar functions include append (above) and cat.
axisvalues
Signature: ([o,nc]a(n))
Internal routine
axisvalues
is the internal primitive that implements axisvals and alters its argument.
axisvalues does not process bad values. It will set the badvalue flag of all output piddles if the flag is set for any of the input piddles.
random
Constructor which returns piddle of random numbers
$a = random([type], $nx, $ny, $nz,...);
$a = random $b;
etc (see zeroes).
This is the uniform distribution between 0 and 1 (assumedly excluding 1 itself). The arguments are the same as zeroes
(q.v.)  i.e. one can specify dimensions, types or give a template.
You can use the perl function srand to seed the random generator. For further details consult Perl's srand documentation.
randsym
Constructor which returns piddle of random numbers
$a = randsym([type], $nx, $ny, $nz,...);
$a = randsym $b;
etc (see zeroes).
This is the uniform distribution between 0 and 1 (excluding both 0 and 1, cf random). The arguments are the same as zeroes
(q.v.)  i.e. one can specify dimensions, types or give a template.
You can use the perl function srand to seed the random generator. For further details consult Perl's srand documentation.
grandom
Constructor which returns piddle of Gaussian random numbers
$a = grandom([type], $nx, $ny, $nz,...);
$a = grandom $b;
etc (see zeroes).
This is generated using the math library routine ndtri
.
Mean = 0, Stddev = 1
You can use the perl function srand to seed the random generator. For further details consult Perl's srand documentation.
vsearch
Signature: ( vals(); xs(n); [o] indx(); [\%options] )
Efficiently search for values in a sorted piddle, returning indices.
$idx = vsearch( $vals, $x, [\%options] );
vsearch( $vals, $x, $idx, [\%options ] );
vsearch performs a binary search in the ordered piddle $x
, for the values from $vals
piddle, returning indices into $x
. What is a "match", and the meaning of the returned indices, are determined by the options.
The mode
option indicates which method of searching to use, and may be one of:
sample

invoke vsearch_sample, returning indices appropriate for sampling within a distribution.
insert_leftmost

invoke vsearch_insert_leftmost, returning the leftmost possible insertion point which still leaves the piddle sorted.
insert_rightmost

invoke vsearch_insert_rightmost, returning the rightmost possible insertion point which still leaves the piddle sorted.
insert_match

invoke vsearch_match, returning the index of a matching element, else (insertion point + 1)
insert_bin_inclusive

invoke vsearch_bin_inclusive, returning an index appropriate for binning on a grid where the left bin edges are inclusive of the bin. See below for further explanation of the bin.
insert_bin_exclusive

invoke vsearch_bin_exclusive, returning an index appropriate for binning on a grid where the left bin edges are exclusive of the bin. See below for further explanation of the bin.
The default value of mode
is sample
.
vsearch_sample
Signature: (vals(); x(n); indx [o]idx())
Search for values in a sorted array, return index appropriate for sampling from a distribution
$idx = vsearch_sample($vals, $x);
$x
must be sorted, but may be in decreasing or increasing order.
vsearch_sample returns an index I for each value V of $vals
appropriate for sampling $vals
I has the following properties:
if
$x
is sorted in increasing orderV <= x[0] : I = 0 x[0] < V <= x[1] : I s.t. x[I1] < V <= x[I] x[1] < V : I = $x>nelem 1
if
$x
is sorted in decreasing orderV > x[0] : I = 0 x[0] >= V > x[1] : I s.t. x[I] >= V > x[I+1] x[1] >= V : I = $x>nelem  1
If all elements of $x
are equal, I = $x>nelem  1.
If $x
contains duplicated elements, I is the index of the leftmost (by position in array) duplicate if V matches.
This function is useful e.g. when you have a list of probabilities for events and want to generate indices to events:
$a = pdl(.01,.86,.93,1); # Barnsley IFS probabilities cumulatively
$b = random 20;
$c = vsearch_sample($b, $a); # Now, $c will have the appropriate distr.
It is possible to use the cumusumover function to obtain cumulative probabilities from absolute probabilities.
needs major (?) work to handles bad values
vsearch_insert_leftmost
Signature: (vals(); x(n); indx [o]idx())
Determine the insertion point for values in a sorted array, inserting before duplicates.
$idx = vsearch_insert_leftmost($vals, $x);
$x
must be sorted, but may be in decreasing or increasing order.
vsearch_insert_leftmost returns an index I for each value V of $vals
equal to the leftmost position (by index in array) within $x
that V may be inserted and still maintain the order in $x
.
Insertion at index I involves shifting elements I and higher of $x
to the right by one and setting the now empty element at index I to V.
I has the following properties:
if
$x
is sorted in increasing orderV <= x[0] : I = 0 x[0] < V <= x[1] : I s.t. x[I1] < V <= x[I] x[1] < V : I = $x>nelem
if
$x
is sorted in decreasing orderV > x[0] : I = 1 x[0] >= V >= x[1] : I s.t. x[I] >= V > x[I+1] x[1] >= V : I = $x>nelem 1
If all elements of $x
are equal,
i = 0
If $x
contains duplicated elements, I is the index of the leftmost (by index in array) duplicate if V matches.
needs major (?) work to handles bad values
vsearch_insert_rightmost
Signature: (vals(); x(n); indx [o]idx())
Determine the insertion point for values in a sorted array, inserting after duplicates.
$idx = vsearch_insert_rightmost($vals, $x);
$x
must be sorted, but may be in decreasing or increasing order.
vsearch_insert_rightmost returns an index I for each value V of $vals
equal to the rightmost position (by index in array) within $x
that V may be inserted and still maintain the order in $x
.
Insertion at index I involves shifting elements I and higher of $x
to the right by one and setting the now empty element at index I to V.
I has the following properties:
if
$x
is sorted in increasing orderV < x[0] : I = 0 x[0] <= V < x[1] : I s.t. x[I1] <= V < x[I] x[1] <= V : I = $x>nelem
if
$x
is sorted in decreasing orderV >= x[0] : I = 1 x[0] > V >= x[1] : I s.t. x[I] >= V > x[I+1] x[1] > V : I = $x>nelem 1
If all elements of $x
are equal,
i = $x>nelem  1
If $x
contains duplicated elements, I is the index of the leftmost (by index in array) duplicate if V matches.
needs major (?) work to handles bad values
vsearch_match
Signature: (vals(); x(n); indx [o]idx())
Match values against a sorted array.
$idx = vsearch_match($vals, $x);
$x
must be sorted, but may be in decreasing or increasing order.
vsearch_match returns an index I for each value V of $vals
. If V matches an element in $x
, I is the index of that element, otherwise it is ( insertion_point + 1 ), where insertion_point is an index in $x
where V may be inserted while maintaining the order in $x
. If $x
has duplicated values, I may refer to any of them.
needs major (?) work to handles bad values
vsearch_bin_inclusive
Signature: (vals(); x(n); indx [o]idx())
Determine the index for values in a sorted array of bins, lower bound inclusive.
$idx = vsearch_bin_inclusive($vals, $x);
$x
must be sorted, but may be in decreasing or increasing order.
$x
represents the edges of contiguous bins, with the first and last elements representing the outer edges of the outer bins, and the inner elements the shared bin edges.
The lower bound of a bin is inclusive to the bin, its outer bound is exclusive to it. vsearch_bin_inclusive returns an index I for each value V of $vals
I has the following properties:
if
$x
is sorted in increasing orderV < x[0] : I = 1 x[0] <= V < x[1] : I s.t. x[I] <= V < x[I+1] x[1] <= V : I = $x>nelem  1
if
$x
is sorted in decreasing orderV >= x[0] : I = 0 x[0] > V >= x[1] : I s.t. x[I+1] > V >= x[I] x[1] > V : I = $x>nelem
If all elements of $x
are equal,
i = $x>nelem  1
If $x
contains duplicated elements, I is the index of the righmost (by index in array) duplicate if V matches.
needs major (?) work to handles bad values
vsearch_bin_exclusive
Signature: (vals(); x(n); indx [o]idx())
Determine the index for values in a sorted array of bins, lower bound exclusive.
$idx = vsearch_bin_exclusive($vals, $x);
$x
must be sorted, but may be in decreasing or increasing order.
$x
represents the edges of contiguous bins, with the first and last elements representing the outer edges of the outer bins, and the inner elements the shared bin edges.
The lower bound of a bin is exclusive to the bin, its upper bound is inclusive to it. vsearch_bin_exclusive returns an index I for each value V of $vals
.
I has the following properties:
if
$x
is sorted in increasing orderV <= x[0] : I = 1 x[0] < V <= x[1] : I s.t. x[I] < V <= x[I+1] x[1] < V : I = $x>nelem  1
if
$x
is sorted in decreasing orderV > x[0] : I = 0 x[0] >= V > x[1] : I s.t. x[I1] >= V > x[I] x[1] >= V : I = $x>nelem
If all elements of $x
are equal,
i = $x>nelem  1
If $x
contains duplicated elements, I is the index of the righmost (by index in array) duplicate if V matches.
needs major (?) work to handles bad values
interpolate
Signature: (xi(); x(n); y(n); [o] yi(); int [o] err())
routine for 1D linear interpolation
( $yi, $err ) = interpolate($xi, $x, $y)
Given a set of points ($x,$y)
, use linear interpolation to find the values $yi
at a set of points $xi
.
interpolate
uses a binary search to find the suspects, er..., interpolation indices and therefore abscissas (ie $x
) have to be strictly ordered (increasing or decreasing). For interpolation at lots of closely spaced abscissas an approach that uses the last index found as a start for the next search can be faster (compare Numerical Recipes hunt
routine). Feel free to implement that on top of the binary search if you like. For out of bounds values it just does a linear extrapolation and sets the corresponding element of $err
to 1, which is otherwise 0.
See also interpol, which uses the same routine, differing only in the handling of extrapolation  an error message is printed rather than returning an error piddle.
needs major (?) work to handles bad values
interpol
Signature: (xi(); x(n); y(n); [o] yi())
routine for 1D linear interpolation
$yi = interpol($xi, $x, $y)
interpol
uses the same search method as interpolate, hence $x
must be strictly ordered (either increasing or decreasing). The difference occurs in the handling of outofbounds values; here an error message is printed.
interpND
Interpolate values from an ND piddle, with switchable method
$source = 10*xvals(10,10) + yvals(10,10);
$index = pdl([[2.2,3.5],[4.1,5.0]],[[6.0,7.4],[8,9]]);
print $source>interpND( $index );
InterpND acts like indexND, collapsing $index
by lookup into $source
; but it does interpolation rather than direct sampling. The interpolation method and boundary condition are switchable via an options hash.
By default, linear or sample interpolation is used, with constant value outside the boundaries of the source pdl. No dataflow occurs, because in general the output is computed rather than indexed.
All the interpolation methods treat the pixels as valuecentered, so the sample
method will return $a>(0)
for coordinate values on the set [0.5,0.5), and all methods will return $a>(1)
for a coordinate value of exactly 1.
Recognized options:
 method

Values can be:
0, s, sample, Sample (default for integer source types)
The nearest value is taken. Pixels are regarded as centered on their respective integer coordinates (no offset from the linear case).
1, l, linear, Linear (default for floating point source types)
The values are Nlinearly interpolated from an Ndimensional cube of size 2.
3, c, cube, cubic, Cubic
The values are interpolated using a local cubic fit to the data. The fit is constrained to match the original data and its derivative at the data points. The second derivative of the fit is not continuous at the data points. Multidimensional datasets are interpolated by the successivecollapse method.
(Note that the constraint on the first derivative causes a small amount of ringing around sudden features such as step functions).
f, fft, fourier, Fourier
The source is Fourier transformed, and the interpolated values are explicitly calculated from the coefficients. The boundary condition option is ignored  periodic boundaries are imposed.
If you pass in the option "fft", and it is a list (ARRAY) ref, then it is a stash for the magnitude and phase of the source FFT. If the list has two elements then they are taken as already computed; otherwise they are calculated and put in the stash.
 b, bound, boundary, Boundary

This option is passed unmodified into indexND, which is used as the indexing engine for the interpolation. Some current allowed values are 'extend', 'periodic', 'truncate', and 'mirror' (default is 'truncate').
 bad

contains the fill value used for 'truncate' boundary. (default 0)
 fft

An array ref whose associated list is used to stash the FFT of the source data, for the FFT method.
one2nd
Converts a one dimensional index piddle to a set of ND coordinates
@coords=one2nd($a, $indices)
returns an array of piddles containing the ND indexes corresponding to the one dimensional list indices. The indices are assumed to correspond to array $a
clumped using clump(1)
. This routine is used in the old vector form of whichND, but is useful on its own occasionally.
Returned piddles have the indx datatype. $indices
can have values larger than $a>nelem
but negative values in $indices
will not give the answer you expect.
pdl> $a=pdl [[[1,2],[1,1]], [[0,3],[3,2]]]; $c=$a>clump(1)
pdl> $maxind=maximum_ind($c); p $maxind;
6
pdl> print one2nd($a, maximum_ind($c))
0 1 1
pdl> p $a>at(0,1,1)
3
which
Signature: (mask(n); indx [o] inds(m))
Returns indices of nonzero values from a 1D PDL
$i = which($mask);
returns a pdl with indices for all those elements that are nonzero in the mask. Note that the returned indices will be 1D. If you feed in a multidimensional mask, it will be flattened before the indices are calculated. See also whichND for multidimensional masks.
If you want to index into the original mask or a similar piddle with output from which
, remember to flatten it before calling index:
$data = random 5, 5;
$idx = which $data > 0.5; # $idx is now 1D
$bigsum = $data>flat>index($idx)>sum; # flatten before indexing
Compare also where for similar functionality.
SEE ALSO:
which_both returns separately the indices of both zero and nonzero values in the mask.
where returns associated values from a data PDL, rather than indices into the mask PDL.
whichND returns ND indices into a multidimensional PDL.
pdl> $x = sequence(10); p $x
[0 1 2 3 4 5 6 7 8 9]
pdl> $indx = which($x>6); p $indx
[7 8 9]
which processes bad values. It will set the badvalue flag of all output piddles if the flag is set for any of the input piddles.
which_both
Signature: (mask(n); indx [o] inds(m); indx [o]notinds(q))
Returns indices of zero and nonzero values in a mask PDL
($i, $c_i) = which_both($mask);
This works just as which, but the complement of $i
will be in $c_i
.
pdl> $x = sequence(10); p $x
[0 1 2 3 4 5 6 7 8 9]
pdl> ($small, $big) = which_both ($x >= 5); p "$small\n $big"
[5 6 7 8 9]
[0 1 2 3 4]
which_both processes bad values. It will set the badvalue flag of all output piddles if the flag is set for any of the input piddles.
where
Use a mask to select values from one or more data PDLs
where
accepts one or more data piddles and a mask piddle. It returns a list of output piddles, corresponding to the input data piddles. Each output piddle is a 1dimensional list of values in its corresponding data piddle. The values are drawn from locations where the mask is nonzero.
The output PDLs are still connected to the original data PDLs, for the purpose of dataflow.
where
combines the functionality of which and index into a single operation.
BUGS:
While where
works OK for most Ndimensional cases, it does not thread properly over (for example) the (N+1)th dimension in data that is compared to an Ndimensional mask. Use whereND
for that.
$i = $x>where($x+5 > 0); # $i contains those elements of $x
# where mask ($x+5 > 0) is 1
$i .= 5; # Set those elements (of $x) to 5. Together, these
# commands clamp $x to a maximum of 5.
It is also possible to use the same mask for several piddles with the same call:
($i,$j,$k) = where($x,$y,$z, $x+5>0);
Note: $i
is always 1D, even if $x
is >1D.
WARNING: The first argument (the values) and the second argument (the mask) currently have to have the exact same dimensions (or horrible things happen). You *cannot* thread over a smaller mask, for example.
whereND
where
with support for ND masks and threading
whereND
accepts one or more data piddles and a mask piddle. It returns a list of output piddles, corresponding to the input data piddles. The values are drawn from locations where the mask is nonzero.
whereND
differs from where
in that the mask dimensionality is preserved which allows for proper threading of the selection operation over higher dimensions.
As with where
the output PDLs are still connected to the original data PDLs, for the purpose of dataflow.
$sdata = whereND $data, $mask
($s1, $s2, ..., $sn) = whereND $d1, $d2, ..., $dn, $mask
where
$data is M dimensional
$mask is N < M dimensional
dims($data) 1..N == dims($mask) 1..N
with threading over N+1 to M dimensions
$data = sequence(4,3,2); # example data array
$mask4 = (random(4)>0.5); # example 1D mask array, has $n4 true values
$mask43 = (random(4,3)>0.5); # example 2D mask array, has $n43 true values
$sdat4 = whereND $data, $mask4; # $sdat4 is a [$n4,3,2] pdl
$sdat43 = whereND $data, $mask43; # $sdat43 is a [$n43,2] pdl
Just as with where
, you can use the returned value in an assignment. That means that both of these examples are valid:
# Used to create a new slice stored in $sdat4:
$sdat4 = $data>whereND($mask4);
$sdat4 .= 0;
# Used in lvalue context:
$data>whereND($mask4) .= 0;
whichND
Return the coordinates of nonzero values in a mask.
WhichND returns the Ndimensional coordinates of each nonzero value in a mask PDL with any number of dimensions. The returned values arrive as an arrayofvectors suitable for use in indexND or range.
$coords = whichND($mask);
returns a PDL containing the coordinates of the elements that are nonzero in $mask
, suitable for use in indexND. The 0th dimension contains the full coordinate listing of each point; the 1st dimension lists all the points. For example, if $mask has rank 4 and 100 matching elements, then $coords has dimension 4x100.
If no such elements exist, then whichND returns a structured empty PDL: an Nx0 PDL that contains no values (but matches, threadingwise, with the vectors that would be produced if such elements existed).
DEPRECATED BEHAVIOR IN LIST CONTEXT:
whichND once delivered different values in list context than in scalar context, for historical reasons. In list context, it returned the coordinates transposed, as a collection of 1PDLs (one per dimension) in a list. This usage is deprecated in PDL 2.4.10, and will cause a warning to be issued every time it is encountered. To avoid the warning, you can set the global variable "$PDL::whichND" to 's' to get scalar behavior in all contexts, or to 'l' to get list behavior in list context.
In later versions of PDL, the deprecated behavior will disappear. Deprecated list context whichND expressions can be replaced with:
@list = $a>whichND>mv(0,1)>dog;
SEE ALSO:
which finds coordinates of nonzero values in a 1D mask.
where extracts values from a data PDL that are associated with nonzero values in a mask PDL.
pdl> $a=sequence(10,10,3,4)
pdl> ($x, $y, $z, $w)=whichND($a == 203); p $x, $y, $z, $w
[3] [0] [2] [0]
pdl> print $a>at(list(cat($x,$y,$z,$w)))
203
setops
Implements simple set operations like union and intersection
Usage: $set = setops($a, <OPERATOR>, $b);
The operator can be OR
, XOR
or AND
. This is then applied to $a
viewed as a set and $b
viewed as a set. Set theory says that a set may not have two or more identical elements, but setops takes care of this for you, so $a=pdl(1,1,2)
is OK. The functioning is as follows:
OR

The resulting vector will contain the elements that are either in
$a
or in$b
or both. This is the union in set operation terms XOR

The resulting vector will contain the elements that are either in
$a
or$b
, but not in both. This isUnion($a, $b)  Intersection($a, $b)
in set operation terms.
AND

The resulting vector will contain the intersection of
$a
and$b
, so the elements that are in both$a
and$b
. Note that for convenience this operation is also aliased to intersect
It should be emphasized that these routines are used when one or both of the sets $a
, $b
are hard to calculate or that you get from a separate subroutine.
Finally IDL users might be familiar with Craig Markwardt's cmset_op.pro
routine which has inspired this routine although it was written independently However the present routine has a few less options (but see the exampels)
You will very often use these functions on an index vector, so that is what we will show here. We will in fact something slightly silly. First we will find all squares that are also cubes below 10000.
Create a sequence vector:
pdl> $x = sequence(10000)
Find all odd and even elements:
pdl> ($even, $odd) = which_both( ($x % 2) == 0)
Find all squares
pdl> $squares= which(ceil(sqrt($x)) == floor(sqrt($x)))
Find all cubes (being careful with roundoff error!)
pdl> $cubes= which(ceil($x**(1.0/3.0)) == floor($x**(1.0/3.0)+1e6))
Then find all squares that are cubes:
pdl> $both = setops($squares, 'AND', $cubes)
And print these (assumes that PDL::NiceSlice
is loaded!)
pdl> p $x($both)
[0 1 64 729 4096]
Then find all numbers that are either cubes or squares, but not both:
pdl> $cube_xor_square = setops($squares, 'XOR', $cubes)
pdl> p $cube_xor_square>nelem()
112
So there are a total of 112 of these!
Finally find all odd squares:
pdl> $odd_squares = setops($squares, 'AND', $odd)
Another common occurance is to want to get all objects that are in $a
and in the complement of $b
. But it is almost always best to create the complement explicitly since the universe that both are taken from is not known. Thus use which_both if possible to keep track of complements.
If this is impossible the best approach is to make a temporary:
This creates an index vector the size of the universe of the sets and set all elements in $b
to 0
pdl> $tmp = ones($n_universe); $tmp($b) .= 0;
This then finds the complement of $b
pdl> $C_b = which($tmp == 1);
and this does the final selection:
pdl> $set = setops($a, 'AND', $C_b)
intersect
Calculate the intersection of two piddles
Usage: $set = intersect($a, $b);
This routine is merely a simple interface to setops. See that for more information
Find all numbers less that 100 that are of the form 2*y and 3*x
pdl> $x=sequence(100)
pdl> $factor2 = which( ($x % 2) == 0)
pdl> $factor3 = which( ($x % 3) == 0)
pdl> $ii=intersect($factor2, $factor3)
pdl> p $x($ii)
[0 6 12 18 24 30 36 42 48 54 60 66 72 78 84 90 96]
AUTHOR
Copyright (C) Tuomas J. Lukka 1997 (lukka@husc.harvard.edu). Contributions by Christian Soeller (c.soeller@auckland.ac.nz), Karl Glazebrook (kgb@aaoepp.aao.gov.au), Craig DeForest (deforest@boulder.swri.edu) and Jarle Brinchmann (jarle@astro.up.pt) All rights reserved. There is no warranty. You are allowed to redistribute this software / documentation under certain conditions. For details, see the file COPYING in the PDL distribution. If this file is separated from the PDL distribution, the copyright notice should be included in the file.
Updated for CPAN viewing compatibility by David Mertens.