On Wed, Aug 10, 2011 at 3:49 PM, Matthew Kenworthy
<[email protected]> wrote:
> This looks good to me.... can it be put in the next version?
Yes, but since I think it should go in PDL::Primitive alongside
where() we'll need documentation for whereND, an update to
the documentation for where, and some tests added. Here is
the start towards that. Save it in a whereND.pdl file and
you should be good to go...
use strict;
=head2 whereND
=for ref
where with support for ND masks and threading
C<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.
C<whereND> differs from C<where> in that the mask
dimensionality is preserved which allows for
proper threading of the selection operation over
higher dimensions.
=for usage
$sdata = whereND $data, $mask
@sdata = whereND $data1, $data2, ..., $mask
where
$data is M dimensional
$mask is N < M dimensional
dims($data) 1..N == dims($maks) 1..N
with threading over N+1 to M dimensions
=for example
$data = sequence(4,3,2); # example data array
$mask4 = (random(4)>0.5); # example 1-D mask array, has $n4 true values
$mask43 = (random(4,3)>0.5); # example 2-D 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
=cut
sub whereND {
my $mask = pop @_; # $mask has 0==false, 1==true
my @to_return;
foreach my $arr (@_) {
my $n = sum($mask);
my $sub_i = $mask * ones($arr);
my $where_sub_i = where $arr, $sub_i;
# count the number of dims in $mask and $arr
# $mask = a b c d e f.....
my @idims = dims($arr);
# ...and pop off the number of dims in $mask
foreach ( dims($mask) ) { shift(@idims) };
my $ndim = 0;
foreach my $id ($n, @idims[0..($#idims-1)]) {
$where_sub_i = $where_sub_i->splitdim($ndim++,$id);
}
push @to_return, $where_sub_i;
}
return (@to_return == 1) ? $to_return[0] : @to_return;
}
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