perlhashkey

In a large Perl hash, how do I extract a subset of particular keys?

I have a large hash and have a subset of keys that I want to extract the values for, without having to iterate over the hash looking for each key (as I think that will take too long).

I was wondering if I can use grep to grab a file with a subset of keys? For example, something along the lines of:

 my @value = grep { defined $hash{$_}{subsetofkeysfile} } ...;
Solution

  • The easiest way is to use a hash slice:

    my @values_subset = @hash{@keys_subset};

    If the hash may not contain some keys from the subset, use a hash slice and grep() to filter out undefs:

    my @values_subset = grep defined, @hash{@keys_subset};