grep { } positional number of element

leszekdubiel has asked for the wisdom of the Perl Monks concerning the following question:

Replies are listed 'Best First'.
Re: grep { } positional number of element by Your Mother (Archbishop) on Oct 23, 2022 at 21:23 UTC
`grep` only goes through the actual elements of whatever is passed to it. No index is passed. You might want something like– `my @myArray = qw(alfa beta gamma); grep { print "$myArray[$_] at $_\n" } 0 .. $#myArray;` [download] But that is atrocious style. `grep` is for filtering, not iterating. Use a `for` loop instead. Terse postfix version, you should generally prefer the expanded with a block– `print "$myArray[$_] at $_\n" for 0 .. $#myArray;` [download]	[reply] [d/l] [select]
Re^2: grep { } positional number of element by Fletch (Bishop) on Oct 24, 2022 at 02:12 UTC
Seconding the style condemnation; similarly using map would be just as incorrect. Use grep to filter, map to transform, and for to iterate (or one of the `List::*` modules for anything else more specialized like a reduce). The cake is a lie. The cake is a lie. The cake is a lie.	[reply] [d/l]
Re: grep { } positional number of element by sectokia (Friar) on Oct 23, 2022 at 21:35 UTC
grep is wrong thing to use here, you could use each: `my @array = ( "Alfa","beta","gamma"); while (my ($index, $element) = each(@array)) { print "$index => $element\n"; }` [download] Output: `0 => Alfa 1 => beta 2 => gamma` [download]	[reply] [d/l] [select]
Re^2: grep { } positional number of element by ibm1620 (Hermit) on Oct 23, 2022 at 22:27 UTC
Or, if you are running the latest version of Perl, v5.36, you could go experimental and use the new for list and indexed function> `use v5.36; use builtin qw/indexed/; no warnings q/experimental::builtin/; no warnings q/experimental::for_list/; my @array = ( "Alfa","beta","gamma"); for my ($index, $element) (indexed @array) { print "$index => $element\n"; }` [download] (Incidentally, is there any difference between indexed(@array) and each(@array)?)	[reply] [d/l]
Re^2: grep { } positional number of element by Your Mother (Archbishop) on Oct 23, 2022 at 23:45 UTC
++ 12 years of using 5.8 broke my brain. I didn’t even remember you could use `each` on arrays now.	[reply] [d/l]
Re^2: grep { } positional number of element by Bod (Parson) on Oct 23, 2022 at 22:29 UTC
you could use each Thank you for the reminder... Just the other day I had a situation where `each` (called on a hash) would have been a good solution. But I completely forgot about its existence having not looked at it for many, many years. I don't think I have ever used `each` but certainly need to ensure I don't forget it again!	[reply] [d/l] [select]
Re^3: grep { } positional number of element by bliako (Abbot) on Oct 24, 2022 at 13:22 UTC
I think there is, or, at least, was, good reason why `each` was erased from our concsiousness. I do not know what the state of these bugs is today. I was definetely bitten by its non-reentrancy /sic/ several times in nested `each` loops.	[reply] [d/l] [select]
Re^4: grep { } positional number of element by Bod (Parson) on Oct 25, 2022 at 16:35 UTC
Re^5: grep { } positional number of element by LanX (Saint) on Oct 25, 2022 at 16:53 UTC
Re^2: grep { } positional number of element by bliako (Abbot) on Oct 24, 2022 at 13:31 UTC
I did not know that, thanks.	[reply]
Re: grep { } positional number of element by jo37 (Curate) on Oct 23, 2022 at 21:52 UTC
Or, if you dislike loops: `use v5.16; use List::MoreUtils 'reduce_u'; my @array = qw(alpha beta gamma); reduce_u {say "at position $_ there is $b"} @array;` [download] Greetings, -jo `$gryYup$d0ylprbpriprrYpkJl2xyl~rzg??P~5lp2hyl0p$`	[reply] [d/l]
Re: grep { } positional number of element by LanX (Saint) on Oct 23, 2022 at 22:14 UTC
As others already explained you showed the equivalent of a `foreach` in JS but asked for a `grep`, where at best a `map` would make sense. And you already got excellent replies! But for completeness Perl is flexible enough to create your own syntactic sugar for this task `use v5.12; use warnings; use Data::Dump qw/pp dd/; our $c; # count sub cmap(&@) { my $block = shift @_ ; local $c=-1; map { $c++; &$block } @_; } # -------- DEMO my @myArray = qw(alfa beta gamma); say "--- used as loop"; cmap { say "at position $c there is $_" } @myArray; say "--- used as map"; dd cmap { [ $c => $_] } @myArray;` [download] ---> `--- used as loop at position 0 there is alfa at position 1 there is beta at position 2 there is gamma --- used as map ([0, "alfa"], [1, "beta"], [2, "gamma"])` [download] Cheers Rolf _{(addicted to the 𐍀𐌴𐍂𐌻 Programming Language :) Wikisyntax for the Monastery}	[reply] [d/l] [select]
Re: grep { } positional number of element by tybalt89 (Monsignor) on Oct 23, 2022 at 22:47 UTC
`#!/usr/bin/perl use strict; # https://perlmonks.org/?node_id=11147614 use warnings; use List::AllUtils qw( pairwise ); my @myArray = qw(alfa beta gamma); pairwise { warn "at position $a there is $b\n" } @{[ 0 .. $#myArray ]}, @myArray;` [download]	[reply] [d/l]
Re: grep { } positional number of element by tybalt89 (Monsignor) on Oct 23, 2022 at 23:45 UTC
In plain old ordinary basic perl (whatever that is) I'd just do: `#!/usr/bin/perl use strict; # https://perlmonks.org/?node_id=11147614 use warnings; my @myArray = qw(alfa beta gamma); warn "at position $_ there is $myArray[$_]\n" for 0 .. $#myArray;` [download]	[reply] [d/l]