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Re: Array indices

by jkahn (Friar)
on Sep 14, 2002 at 05:53 UTC ( [id://197804]=note: print w/replies, xml ) Need Help??


in reply to Array indices

Your indices function sounds sorta like the smart match code that I heard theDamian talk about at his Perl6 talk -- well, at least knowing whether "heimer" is in the list.

Of course, you could write your own indices() function pretty quickly, using a sort of modification of the Schwartzian Transform (I actually have tested this, on a few cases, but let me know if I've missed anything): 

sub indices ($@) {
  # note the prototype has target, then list
  my $target = shift;
  my (@list) = @_;

  my $index = 0;
  map { $_->[1] }
    grep { $_->[0] eq $target }
      map { [$_ , $index++] } @list;
}

[download]

I'm sure some wizard out there could tighten this up, but I think it's pretty clear what I'm aiming at.

Replies are listed 'Best First'.
Re^2: Array indices
by Aristotle (Chancellor) on Sep 14, 2002 at 06:00 UTC
    I wouldn't use a prototype here. They're much more headache than they're usually worth. 
    sub indices {
    my $match = shift;

    my $i = 0;
    map { $i++; $_ eq $match ? $i : () } @_
}

    [download]

    Returning an empty list in the map callback causes that iteration to disappear from the result list. This is useful because you can use it as a surrogate grep that allows you to return something other than what your input was.

    Update: removed ->[0] copy paste remainder from code.

    Update 2: the following is more idiomatic and pretty much makes having a separate sub useless. We're back to grep too:

    sub indices {
    my $match = shift;
    grep $_[$_] eq $match, 0 .. $#_
}

    [download]

    Makeshifts last the longest.

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