my @data = ( [ 'a', 2 ],
             [ 'b', 5 ],
             [ 'b', 2 ],
             [ 'c', 8 ] );

# Keep data sorted on keys.
@data = sort { $a->[0] cmp $b->[0] } @data;

# Get list of values in order
@values = map { $_->[1] } @data;

# Operate on values, in order
{ $_->[1] =* 2 } foreach ( @data );