Re: How to grep for values & see the keys?

TIMTOWTDI!

But instead of reinventing the wheel, there is a pairgrep and pairmap in (newer°) List::Util, which is core

debugger-demo (via perl -de0 )

  DB<10> @h{1..26} = a..z

  DB<11> use List::Util qw/pairgrep/

  DB<12> x pairgrep { $b =~ /[aeiou]/ } %h
0  15
1  'o'
2  21
3  'u'
4  9
5  'i'
6  5
7  'e'
8  1
9  'a'
  DB<13> use List::Util qw/pairmap/

  DB<14> x pairmap { $b =~ /[aeiou]/ ? [$a => $b] : () } %h
0  ARRAY(0x349eed8)
   0  15
   1  'o'
1  ARRAY(0x349ef20)
   0  21
   1  'u'
2  ARRAY(0x349ef80)
   0  9
   1  'i'
3  ARRAY(0x349efe0)
   0  5
   1  'e'
4  ARRAY(0x349f040)
   0  1
   1  'a'
  DB<15>
[download]

update

Perl doesn't have datatype for pairs, but you could use a second hash for shorter syntax :)

  DB<15> %h2 = pairgrep { $b =~ /[aeiou]/ } %h

  DB<16> x \%h2
0  HASH(0x349ee60)
   1 => 'a'
   15 => 'o'
   21 => 'u'
   5 => 'e'
   9 => 'i'
  DB<17>
[download]

update

°) came into core with 5.20.0 i.e. since May 27, 2014. So only new for oldies like me ;-)

Cheers Rolf
_{(addicted to the Perl Programming Language :)

Wikisyntax for the Monastery}

Comment on Re: How to grep for values & see the keys? Select or Download Code

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Re^2: How to grep for values & see the keys? by kcott (Archbishop) on May 14, 2022 at 02:25 UTC
G'day Rolf, "°) came into core with 5.20.0 i.e. since May 27, 2014. So only new for oldies like me ;-)" Just noting that https://perldoc.perl.org/5.20.0/List::Util confirms this; however, https://perldoc.perl.org/5.34.1/List::Util has "Since version 1.29." for both `pairgrep` and `pairmap`. I recalled doing some limited investigation into this last month: "Re: Dancer app works until I run it with Plack::Handler::Apache2" (see the last two dot points under "Other suggestions:"). I now note that https://perldoc.perl.org/5.34.1/List::Util#KNOWN-BUGS lists "RT #95409" while https://perldoc.perl.org/5.20.0/List::Util#KNOWN-BUGS does not. There are quite a few other functions with "Since version 1.xx." — probably worth checking when `List::Util` is used; especially if bugs are detected or unexpected behaviours are encountered. — Ken	[reply] [d/l] [select]
Re^3: How to grep for values & see the keys? by LanX (Saint) on May 15, 2022 at 23:08 UTC
Hi Ken Thanks for pointing to the bug, that's indeed an ugly case ... > however, https://perldoc.perl.org/5.34.1/List::Util has "Since version 1.29." for both pairgrep and pairmap. That's the modules version, 5.20.0 comes bundled with 1.38 (look at upper right corner) > I now note that https://perldoc.perl.org/5.34.1/List::Util#KNOWN-BUGS lists "RT #95409" while https://perldoc.perl.org/5.20.0/List::Util#KNOWN-BUGS does not. 5.34.1 comes bundled with v1.55 of List::Util ... I assume the bug was discovered and included later. Cheers Rolf _{(addicted to the Perl Programming Language :) Wikisyntax for the Monastery}	[reply]
Re^4: How to grep for values & see the keys? by kcott (Archbishop) on May 16, 2022 at 03:53 UTC
I was aware that `1.xx` referred to module versions. I wasn't aware that the version number was displayed in Perldoc: good to know; thanks for enlightening me. — Ken	[reply] [d/l]
Re^2: How to grep for values & see the keys? by misterperl (Friar) on May 13, 2022 at 14:18 UTC
Rolf as the song goes- YOU ARE SIMPLY THE BEST.. Whenever I see your name in a reply, I rejoice! Curiously, I was on the right track because I was looking at `List::Util qq(pairs)` to solve this but it only seemed to work on arrays. I didn't see pairgrep , looks very useful. I'll try that today after studying your example.	[reply] [d/l]