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Re: Help me not use codefor($i=0;$i=$#array;$i++)/code...Please!

by btrott (Parson)
on Jun 21, 2001 at 01:48 UTC ( #90212=note: print w/ replies, xml ) Need Help??


in reply to Help me not use for($i=0;$i=$#array;$i++)...Please!

Is that code an example or is that the specific instance you're trying to replace? Because if the latter, you can just use grep:

my @array = grep $_ != 5, 0..9;
Actually this isn't exactly the same, because your code has a bug, assuming that your goal is to weed out elements equal to 5. (That's the goal, right? If not, never mind.)

The bug is that you're altering the array while progressing through the loop, which means that you skip certain elements. Try your code on this array:

my @array = qw(0 1 2 3 4 5 5 6 7 8 9 );
Only the first 5 will be removed, because after splice-ing out the first 5, the index of the 5 following it has just decreased by 1. But the loop counter increments, and you end up skipping the 5 following it.

As for your general question, which seems to be, is there a way to get rid of reliance on loop counters when iterating through arrays. And that's a good question, and I don't really think there is a good way. There isn't a magic variable for "index into an array" when in a foreach loop. Although perhaps there should be; Dominus has a post about this.

All the same, though, you should probably refrain from altering an array while iterating over it.


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Re: Re: Help me not use codefor($i=0;$i=$#array;$i++)/code...Please!
by IraTarball (Monk) on Jun 21, 2001 at 02:13 UTC
    This was an extremely simplified example to try and get to the core problem. In reality this is an array of arrays inside a hash. I'm looping through doing some processing and certain things should only be processed once but others should be processed multiple times. My solution was to remove them from the array after processing if they were to only be processed once.
    After looking at all the great responses here I think @array = grep $_ != 5, @array; is what I want. The 5 would actually be an array reference, but I think this will work.

    Thanks for all the help,
    Ira.

    "So... What do all these little arrows mean?"
    ~unknown

      If you bracket it, the grep expression becomes a block. It can be as complicated as you please. If it evaluates true, $_ (possibly modified within the block) is placed in the returned array.

      After Compline,
      Zaxo

      Update: Corrected block <-> expr terminology.

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