in reply to Re: Elegantly Selecting Every 3rd Element in an Array.
in thread Elegantly Selecting Every 3rd Element in an Array.

Without the extra variable declaration:
my @every_3rd = @array[grep { ! (($_+1) % 3) } 0..$#array];

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Update: Fixed (due to jerrygarciuh's catch). Nothing like untested code. And precedence. (though looking at the precedence table in perlop, it looks like what I had (in jerry's node below) should've worked. Bug? Can someone explain?).

Another update:tye explains below. Though I think precedence of parens should differ between 'functions' and 'operators'. Oh well...

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Re: Re: Re: Elegantly Selecting Every 3rd Element in an Array.
by jerrygarciuh (Curate) on Sep 29, 2001 at 02:37 UTC
    Runrig,
    Well, maybe I botched it, but all I did was change @array to my var @a like so:
    my @a=qw(las vegas every saturday night third is my element);
my @every_3rd = @a[grep { not ($_+1) % 3 } 0..$#a];
print "@every_3rd";

    [download]
    and tell it to print and it runs without error but prints nothing.
    ???
    jg

    Ain't no time to hate! Barely time to wait! ~RH
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[d/l]
      It prints nothing because you have a precedence problem

      not ($_+1) % 3

      Will always evaluate to false as it is the same as

      (not ($_+1)) % 3

      Adding some parens in the right places

      not (($_+1) % 3)

      Should give the correct result

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[d/l]
[select]
        Why do the parens change the precedence of the 'not'?? Seems like 'not' should still have the lowest precedence. Compare these two (which should return every third element, but start with the first), and tell me why they should be different:
        not $_ % 3
not ($_) % 3

        [download]
        Update:tye explains below. My opinion (on current precedence rules, not tye's opinion) above.
[reply]
[d/l]

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