Delete keys from hash map in perl which matches values from array

Question

I would like to use Perl to delete keys from a hash map that match values in a given array.

Example:

Input:

   @array = ("apple", "banana" , "cherry")
   %hash = ( '/abc/apple/somestring' => val1,
             '/banana/somestring/somesting' => val2,
             '/xyz/apple/somestring'   => val3,
             '/somestring/somestring/'        => val4,
             '/xyz/somestring/random'        => val2,
           )

Output:

   %hash = ( '/somestring/somestring/'        => val4,
             '/xyz/somesting/random'        => val2,
           )

amon · Accepted Answer · 2013-07-22 21:48:34Z

4

Simple:

For each element in the array, select the matching hash keys

for my $elem (@array) {
  my @matching_keys = grep { 0 <= index $_, $elem } keys %hash;

Then, delete the hash entries with the matching keys:
```
  delete @hash{@matching_keys};
}
```

The 0 <= index $_, $elem could also be written as /\Q$elem/, if you are optimising for readability instead of speed.

Alternatively: build a regex that matches all elems in the array:

my $rx = join '|', map quotemeta, @array;

Then, select and delete all keys that match this regex:

my @matching_keys = grep /$rx/, keys %hash;
delete @hash{@matching_keys};

This should be more efficient.

answered Jul 22, 2013 at 21:48

amon

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2 Comments

jp922898 Over a year ago

That works like a charm. I was iterating using foreach loop and it didn't work.

gaussblurinc Over a year ago

@amon, bravo! the best tip that I've read today :) delete + slices! bravo!

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