A wee implementation of Haskell's zip() in perl (also available via Language::Functional). Update - now maintains list order.
sub zip {
  my($l1, $l2) = @_;
  die "zip(): expects two ARRAY refs\n"
    if ref($l1) ne 'ARRAY' or ref($l2) ne 'ARRAY';
  my %ret; @ret{ @$l1 } = @$l2;
  return map { $_ => $ret{$_} } @$l1;
}

[download]

Replies are listed 'Best First'.
Re: a little zip()
by jmcnamara (Monsignor) on Apr 10, 2003 at 15:30 UTC

    Here is a variation that maintains order. I've used your code structure and syntax: 
        sub zip2 {
        my($l1, $l2) = @_;
        die "zip(): expects two ARRAY refs\n"
          if ref($l1) ne 'ARRAY' or ref($l2) ne 'ARRAY';

        return (@$l1, @$l2)[map {$_, $_+@$l1} 0 .. $#$l1];
    }

    [download]

    --
    John.

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[d/l]
Re: a little zip()
by DrHyde (Prior) on Apr 25, 2003 at 12:52 UTC
    Here's one which zip()s an arbitrary number of arrays. If any of the arrays don't have enough elements, we pad with the empty string, cos that's what I needed at the time. Changing it to emit undefs would be trivial: 
    sub zipn {
    local $[ = 0;
    [
        map {
            my $index = $_;
            map {
                defined($_[$_][$index]) ?
                    $_[$_][$index] :
                    ''
            } 0..$#_
        } 0 .. maximum(map { $#{$_[$_]} } 0..$#_)
    ]
}

sub maximum {
    local $[ = 0;
    ($#_ == 1) ?
        (
            ($_[0] >= $_[1]) ?
                $_[0] :
                $_[1]
        ) :
        maximum(maximum($_[0], $_[1]), @_[2..$#_]);
}

    [download]
    Call it like so: 
    zipn([1,2,3], [4,5,6], [7,8,9,10])

    [download]
    and it'll return this: 
    [1,4,7,2,5,8,3,6,9,'','',10]

    [download]
    That maximum() function is a bit silly, getting rid of the recursion would make it way more efficient, but I firmly believe that "to recurse is divine".
[reply]
[d/l]
[select]
Re: a little zip()
by diotalevi (Canon) on Apr 10, 2003 at 15:25 UTC

    How about returning a reference instead? Its lighter weight and can actually be treated as a hash without having to be assigned into one. Or is that part of the meaning of zip() - to return an interleaved list?

[reply]
      Or is that part of the meaning of zip() - to return an interleaved list?
      Yup, it zips 2 lists together, much like the zipper on a real world zip interleaves the teeth of the zip together :) I've just used a hash there as that was the shortest way I could think of interleaving two lists, even though it might not be the best way (doesn't check for the length of the lists for starters).
      HTH

      _________
      broquaint

[reply]

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