How should I delete hash elements while iterating?

Question

I have fairly large hash (some 10M keys) and I would like to delete some elements from it.

I usually don\'t like to use delete or splice, a

Answer 1

Based on the example in the question, you could use a grep to filter out the keys that match your $key token.

Update

Your comment has clarified your need. My suggestion would be to determine the indexes that match your requirement and update you @keys set accordingly. The idea is to update @keys while looping over it so that unnecessary iterations are avoided.

I've implemented the simple grep as a customizable function here.

sub matches { $_[0] =~ /$_[1]/ ? 1 : 0 }  # Simple grep implemented here

my @keys = keys %hash;  # @keys should initially contain all keys

while ( @keys ) {

    my $key = shift @keys;
    next unless should_be_deleted ($key);  # Skip keys that are wanted

    my @indexes_to_delete = grep { matches ($key, qr/$keys[$_]/) } 0 .. $#keys;

    delete @hash { @keys[@indexes_to_delete] };     # Remove the unwanted keys

    splice @keys, $_, 1 foreach @indexes_to_delete; # Removes deleted ...
                                                    # ... elements from @keys.
                                                    # Avoids needless iterations.
}