This really isn't a homework problem. Honest.

In the following: 

#!/bin/env perl
my %hash = (one => 1, two => 1, three => 1);
map { $hash{$_} = 0 } ('two', 'three');

[download]
$hash{one} is the only key whose value not set to zero. How can map be used to change this value, but not any others given the same ('two', 'three') list?

In reply to performing operation on elements not in list? by Anonymous Monk

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