See Two handy tools for nested arrays: mapat and transpose and Transpose a matrix of chars for some ideas. I don't think you would need the number crunching power of PDL for a simple transpose. See Math-Matrix

There are also some snippets laying around in old nodes, for taking slices from 2-d arrays, you could just take slices and use it to convert from rows to columns or vice-versa.

Here is one I have handy( use Super Search)

#!/usr/bin/perl
# 2-d array-slice

my @arr = (['a','b','c'],
          ['h','i','j'],
          ['x','y','z']);

print map $_->[1], @arr;
print "\n";
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