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How do I modify the KEYS in a hash (copy)

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Contributed by NetWallah on Jul 21, 2004 at 21:38 UTC
Q&A  > hashes


Description:

How to replace the spaces with underscores, in the Keys of a hash? (Or perform other transformation on the KEYS ?)

Answer: How do I modify the KEYS in a hash (copy)
contributed by NetWallah

To modify keys of a hash, it is necessary to copy it. The keys can be modified in the process of the copy by using 'map' like this:

my %Orig=('a b'=>44, 'c d'=>22, rr=>99); my %Copy = map {my $y=$Orig{$_}; #Save Copy of Val tr/ /_/; $_ => $y} keys %Orig; print qq(C: $_ => $Copy{$_}\n) for keys %Copy; print qq(O: $_ => $Orig{$_}\n) for keys %Orig;
The trick here is to save a copy of the Value into "$y" before "$_" is modified.
Once $_ is modified, the $Orig{$_} is no longer valid, so it must be saved into $y first.
Answer: How do I modify the KEYS in a hash (copy)
contributed by jdporter

my %Copy; @Copy{ map { tr/ /_/; $_ } keys %Orig } = values %Orig;
Answer: How do I modify the KEYS in a hash (copy)
contributed by NetWallah

Here is another way to modify KEYS in-place.

This would be efficient in the case where there were a relatively small number of keys that required modification.

Use the previous method (copy the hash) if the number of keys requiring modification is large.

my %o=(this=>33, 'th at'=>44, other=>55,'some thing'=>66,'or another'= +>77,none=>88); while (my ($k,$v)=each %o){ my $ModifiedK = $k; next unless $ModifiedK =~s/\s/_/; delete $o{$k}; #This is SAFE !! RTFM. $o{$ModifiedK}=$v; }; print qq(Mod: $_\t=>$o{$_} \n) for sort keys %o"

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