The magic bullet you're looking for is array_reduce()
, e.g. (PHP 5.3+):
list( $left, $right ) = array_reduce( $input,
function( $memo, $item ) {
list( $l, $r ) = explode( '-', $item );
$memo[0][$l] = $memo[1][$r] = true;
return $memo;
},
array( array(), array() )
);
var_dump( array_keys( $left ), array_keys( $right ) );
You can see it in action here.
With PHP <5.3 you'll have to declare the function ahead of time:
function my_reducer( $memo, $item ) {
list( $l, $r ) = // ...
// ... as above ...
}
list( $left, $right ) = array_reduce(
$input, 'my_reducer',
array( array(), array() )
);