No, no. I mean this:

my @actual_data = (
    [ ... ],
    [ ... ],
    [ ... ],
);

my %index_of = (
    foo => 0,
    bar => 1,
    baz => 2,
);

my @key_for = qw( foo bar baz );

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

[download]

When you move things around in @actual_data, you need to the move the keys around in exactly the same fashion in @key_for. You also need to collect all keys whose values changed positions and update them in %index_of accordingly. To just swap two elements, this is trivial:

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

[download]

Reformulating this for atomic operations involving more than two elements is trickier, since the order of operations is then significant, but shouldn't be very hard either.

Makeshifts last the longest.

In reply to Re^3: Re-orderable keyed access structure? by Aristotle
in thread Re-orderable keyed access structure? by BrowserUk

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