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Re: array => hash of occurrence indexes

by kcott (Chancellor)
on Sep 12, 2013 at 05:19 UTC ( #1053646=note: print w/replies, xml ) Need Help??


in reply to array => hash of occurrence indexes

G'day pldanutz,

I generally think it's better to pass around scalars than entire data structures, so returning a reference to that hash would be my preference.

If you wrapped $h{$k} in @{...}, you could dispense with if (! $h {$k}) { $h {$k} = [] } entirely.

Even if you're using 5.012 for other reasons elsewhere in your code, I see little, if any, value in using each here. It's easy to write it for any Perl5.

Putting all that together, you could code occurrences() like this instead:

sub occurences { my %h; my $i = 0; push @{$h{$_}}, $i++ for @_; return \%h; }

If you were looking for a golf answer, you could start with the following and then proceed to remove whitespace until illegibility was achieved. :-)

sub occurences { my ($i, %h) = 0; push @{$h{$_}}, $i++ for @_; \%h }

Here's my tests:

-- Ken

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[Corion]: You'll have to look somewhere esoteric for that. Maybe some tied variable or special dualvar can also trigger that. But it's certainly not a common occurrence
[Corion]: And on 5.20, the following also outputs no find:perl -wle 'for my $x ("\x{2000}".."\ x{1fffff}") { if( $x && ! length $x ) { warn qq(<$x>); warn length $x; die } }'
[Corion]: (this time on Unix)
[hippo]: Understood. I'll have to go through the code and see if it's doing anything fancy with ties, dual-vars or non-scalars. In the end, it's probably a bug though.
[Corion]: Aaah - you should be able to do this with overload, but I would hit somebody really hard if they constructed objects that are true but the empty string, and you not knowing about the domain knowledge where this makes sense
[Eily]: you could tie a variable into not having the same value each time, if you like to make people who try to debug your code facepalm
[Corion]: perl -wle 'package o; use overload q("") => sub {warn "str"; ""}, bool => sub{warn "bool"; 1}; package main; my $o={}; bless $o => o; print "Yay" if ($o && !length($o))'
[Corion]: But people writing such code should document the objects they construct and why it makes sense for an object to be invisible as string while being true in a boolean context
[hippo]: That's equal parts clever and horrendous.

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