use warnings;
use PDL;
use PDL::NiceSlice;

# Here is my matrix:
my $data = sequence(5,5);

print "Original:\n$data\n";

# In order to permute columns, I need a *column* vector with the
# column numbers that I want. (You'd think a *row* vector would be
# more appropriate, but that's not how it works. Alas.)
my $indices = sequence(5);

# Set up to exchange the second and the third column:
#$indices(1:2) .= $indices(2:1);    ### should work but doesn't for me
$indices(1:2) .= $indices(pdl [2,1]);

# Perform the exchange:
my $rearranged = $data->dice_axis(0, $indices);

print "Column swap:\n$rearranged\n";

# Start over and exchange the fourth and fifth rows:
$indices = sequence(5);
$indices(3:4) .= $indices(pdl[4,3]);
my $further_rearranged = $rearranged->dice_axis(1, $indices);

print "Column and row swap:\n$further_rearranged\n";