performing operation on elements not in list?

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

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Re: performing operation on elements not in list? by gwadej (Chaplain) on Jan 09, 2009 at 21:17 UTC
Leaving aside the whole map in void context discussion for a moment, let's take the question a little differently. How would you make a list of the keys that are not in the list `('two', 'three')`? The answer to that is the answer to your question. G. Wade	[reply] [d/l]
Re: performing operation on elements not in list? by ikegami (Patriarch) on Jan 09, 2009 at 21:41 UTC
`my %hash = (one => 1, two => 1, three => 1); my @keep = qw( two three ); my %keep = map { $_ => 1 } @keep; $hash{$_} = 0 for grep !$keep{$_}, keys %hash;` [download]	[reply] [d/l]
Re: performing operation on elements not in list? by setebos (Beadle) on Jan 10, 2009 at 00:11 UTC
Just decide which keys should be kept and which should not: `my %hash = (one => 1, two => 1, three => 1); my %keep; @keep{ qw(two three) } = (); map { exists($keep{$_}) or $hash{$_} = 0 } keys(%hash);` [download]	[reply] [d/l]
Re: performing operation on elements not in list? by johngg (Canon) on Jan 09, 2009 at 21:34 UTC
Like this perhaps `$ perl -le ' > %h = ( one => 1, two => 1, three => 1 ); > $inv = do{ local $" = q{\|}; qr{^@{ [ qw{ two three } ] }$} }; > map $h{ $_ } = 0, grep ! /$inv/, keys %h; > print qq{$_ - $h{ $_ }} for keys %h;' three - 1 one - 0 two - 1 $` [download] Cheers, JohnGG	[reply] [d/l]
Re^2: performing operation on elements not in list? by ikegami (Patriarch) on Jan 09, 2009 at 21:46 UTC
Two errors. You end up with `qr/^two\|three$/` which matches "twoo". You don't convert the keys to regexp If the list of keys to keep is static, you want `my $inv = qr/two\|three/;` [download] If the list of keys to keep is dynamic, you want `my $inv = do{ local $" = q{\|}; qr{@{[ map quotemeta, @keep ]}} };` [download] or the much simpler `my ($inv) = map qr/$_/, join '\|', map quotemeta, @keep;` [download] In all cases, use `/^$inv\z/` in the `grep`.	[reply] [d/l] [select]
Re^3: performing operation on elements not in list? by johngg (Canon) on Jan 09, 2009 at 22:03 UTC
Good catch regarding the anchors and alternation. The OP says "given the same ... list" so the keys not to change are invariable. So I should have said. `$inv = do{ local $" = q{\|}; qr{^(?:@{ [ qw{ two three } ] })$} };` [download] I'm not sure what you mean when you say I don't convert the keys to regexp. Cheers, JohnGG	[reply] [d/l]
Re^4: performing operation on elements not in list? by ikegami (Patriarch) on Jan 09, 2009 at 22:13 UTC
Re^4: performing operation on elements not in list? by ikegami (Patriarch) on Jan 09, 2009 at 22:15 UTC
Re: performing operation on elements not in list? by zentara (Cardinal) on Jan 09, 2009 at 21:20 UTC
It's doing what you tell it to do. `map { $hash{$_} = 0 } (keys %hash);` [download] I'm not really a human, but I play one on earth Remember How Lucky You Are	[reply] [d/l]
Re: performing operation on elements not in list? by JavaFan (Canon) on Jan 10, 2009 at 10:53 UTC
Untested: `my @keep = qw [two three]; my %keep; @keep{@keep} = @hash{@keep}; map {$hash{$_} = 0} for keys %hash; @hash{@keep} = @keep{@keep};` [download]	[reply] [d/l]