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I've got an object method which digs into a hash of arrays of arrays and pulls out the last element of each stored array. Here's my code:

sub whatever
{
  my $self = shift;

  # ... do stuff to set ar_data...

  # Slice out the last element of each stored array into a new array
  my @last_elements;
  push @last_elements, $_->[$#_] for @{$ar_data};
  return \@last_elements;
}
[download]

After grabbing some water, I walked back and realized that @last_elements is (uh-oh) a transitory variable. (and wouldn'tcha know it, I try to look up on the web why transitory variables are bad, and I can't find anything. Dang; I'm sure dominus wrote about this somewhere. Or maybe this is hard water I'm drinking.) So, with a vague idea that some variables are "good" and others are "bad", I wanted to re-write my method to just return the list of @last_elements without actually storing into a list. (Sidenote: or is this foolish? Am I just inviting bogarts into my code?)

After a bit of toying, I realized that there are other ways to iterate over a list than by using for. Enter sort, map, and grep.

#!/usr/bin/perl

use strict;
use warnings;

# fill the 2-d array
my @data;
for ( 0..2 ) {
  push @data, [qw 'a bc def' ];
}

# try extracting last element from each stored array
my @for_data = slice_with_for ( @data );
my @map_data = slice_with_map ( @data );
my @sort_data = slice_with_sort ( @data );
my @grep_data = slice_with_grep ( @data );

# show the y-axis slices
print "for :  @for_data\n";
print "map :  @map_data\n";
print "sort:  @sort_data\n";
print "grep:  @grep_data\n";

exit;


sub slice_with_for
{
  my @slice_me = @_;
  my @last_fields;
  push @last_fields, $_->[2] for @slice_me;
  @last_fields;
}


sub slice_with_map
{
  my @slice_me = @_;
  return map { $_->[2] ? $_->[2] : () } @slice_me;
}


sub slice_with_sort
{
  my @slice_me = @_;
  sort { $a->[2] cmp $b->[2] } @slice_me;
}

sub slice_with_grep
{
  my @slice_me = @data;
  grep { $_->[2] } @slice_me;
}

exit;
[download]

Prints:
for : def def def
map : def def def
sort: ARRAY(0x80fad5c) ARRAY(0x810c844) ARRAY(0x810c7c0)
grep: ARRAY(0x80fad5c) ARRAY(0x810c844) ARRAY(0x810c7c0)

My questions:
1. What other ways are there to iterate over the list besides for, sort, map, and grep?
2. Why don't my slice_with_grep and slice_with_sort functions return what I'm expecting?
3. Am I drunk, or is the water? That is, have I invented this whole notion of a "transitory variable", or is it really something that exists (albeit momentarily) and should be avoided?

blyman
setenv EXINIT 'set noai ts=2'

In reply to seeking different ways to slice a 2-d array by belden

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