How do I undefined the value for a hash key in Perl?

Question

#!/usr/bin/perl

use strict; 
use warnings;

my %hash;

undef($hash{"a"});
undef($hash{"b"});
print scalar values %hash; # i need here 0
print scalar keys %hash; # and here 2

thank you, guys!

Answer 1

undef($hash{"a"});

is equivalent to

$hash{"a"}=undef;

So you add key 'a' with value undef. To delete value from hash use "delete".

delete $hash{"a"};

It is not possible to have different size of 'keys' and 'values' for same hash. You can use grep to filter unwanted elements.

Answer 2

The other answer's point about definedness vs. existence is a very good one, but If you actually do want to know the number of defined values you can always do

print scalar grep { defined $_ } values %hash