Re: alternate array elements

$ perl -E 'say grep {++$i %2} <a b c d e f g>'
aceg
$ perl -E 'say grep {$i++ %2} <a b c d e f g>'
bdf
[download]

They only nasty thing about this solution is that it requires a variable (here $i) in the outer scope

A working Perl 6 solution:

$ perl6 -e 'my @a = "a".."g"; say @a[0, *+2 ... +@a]'
aceg
[download]

An idiomatic Perl 6 solution (but not yet implemented in Rakudo):

@a[0, *+2 ... *]
[download]

Another working Perl 6 solution, which is a variation of the grep theme but without the need of an external variable:

say <a b c d e f g>.pairs.grep({.key !% 2})>>.value
[download]

(Updated: Added Perl 6 examples)

Perl 6 - links to (nearly) everything that is Perl 6.

Comment on Re: alternate array elements Select or Download Code

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Re^2: alternate array elements by mrdvt92 (Acolyte) on May 12, 2023 at 17:39 UTC
With the advent of the new `state` key word in 5.10. I would think this would be the best solution today. `my @odd = grep {state $i=1; $i++ % 2} qw{a 1 b 2 c 3}; my @even = grep {state $i=0; $i++ % 2} qw{a 1 b 2 c 3};` [download] Example `perl -e 'use v5.10; my @odd = grep {state $i=1; $i++ % 2} qw{a 1 b 2 +c 3}; say @odd;'` [download]	[reply] [d/l] [select]
Re^3: alternate array elements by LanX (Saint) on May 12, 2023 at 21:19 UTC
BTW: for one-liners you can use global vars like `$a` or `$b` without declaration, even when strict. `C:\>perl -e"print grep {++$a % 2} qw{a 1 b 2 c 3}" abc` [download] Though their values will leak into the outer scope, so `state` is better for longer scripts. FWIW: I always thought that an automatic loop-count variable `$c` or `$^c` would come very handy inside grep-like constructs. Cheers Rolf _{(addicted to the 𐍀𐌴𐍂𐌻 Programming Language :) Wikisyntax for the Monastery}	[reply] [d/l] [select]