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my @actual_data = (
    [ ... ],
...
my $lookup_by_key = $actual_data[ $index_of{ 'bar' } ];
my $lookup_by_idx = $actual_data[ 1 ];
my $key_from_idx  = $key_for[ 1 ];

sub swap_elements_by_idx {
    my ( $i, $j ) = @_;
...
    @key_for[ $i, $j ] = @key_for[ $j, $i ];
    @index_of{ @key_for[ $i, $j ] } = @index_of{ @key_for[ $j, $i ] };
}