We have: a hash, i.e. mapping from one set to another; a set.
We need to restrict the domain of this mapping to the set and by the set.
Note: the set may not be a subset of the domain of our mapping.

Restriction to the set:

%h1=( 1=>"one", 2 => "two", 3 => "three", 4 => "four");
@set=(1, 3, 5, 7);

my %h2;
$h2{$_} = $h1{$_} for grep exists $h1{$_}, @set;

[download]

Restriction by the set:

%h1=( 1=>"one", 2 => "two", 3 => "three", 4 => "four");
@set=(1, 3, 5, 7);

my %h2 = %h1;
delete $h2{$_} for grep exists $h1{$_}, @set;

[download]

What about the same for values? (restrict the range to the set and by the set)?

In reply to Mapping restrictions by brother ab

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