I'm not sure I understand your requirements. What are the potential contents of the $dec pdl? Will the values of the elements in $dec(:,0) always be 1 or 2? Are you essentially trying to accomplish this: 
#!/usr/bin/env perl
use strict;
use warnings;

use PDL;
use PDL::NiceSlice;

my $dec = pdl [[1,1,2,2,2],[10,15,13,11,4]];
my $min = $dec->(:,0)->minimum;
my $max = $dec->(:,0)->maximum;
my $v = zeroes(2,2);
$v(0,0) .= $min;
$v(0,1) .= $max;
$v(1,0) .= $dec->(:,1)->index(which $dec->(:,0) eq $v(0,0))->maximum;
$v(1,1) .= $dec->(:,1)->index(which $dec->(:,0) eq $v(0,1))->maximum;

print "$v\n";

exit;

[download]
Which results in this output: 
[
 [ 1 15]
 [ 2 13]
]

[download]
Are you trying to find a way to construct $v as a pdl directly without defining the individual elements of $v? I have a hunch that this may be a case of an XY Problem.

In reply to Re: PDL threading where/which instead of loop by kevbot
in thread PDL threading where/which instead of loop by roark

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