How to merge subarray values and remove duplicates?

If you really don't want to loop, try this:

$arr[] = array('A','B');$arr[] = array('C','B');$arr[] = array('C','D');$arr[] = array('F','A');$merged = array_unique(call_user_func_array('array_merge', $arr));

OK through another question I found out that the following is actually possible (I tried myself without success, I had the wrong version) if you use PHP version >= 5.3.0:

$merged_array = array_reduce($arr, 'array_merge', array());

If you only want unique values you can apply array_unique:

$unique_merged_array = array_unique($merged_array);

This works if you only have flat elements in the arrays (i.e. no other arrays). From the documentation:

Note: Note that array_unique() is not intended to work on multi dimensional arrays.

If you have arrays in your arrays then you have to check manually e.g. with array_walk:

$unique_values = array();function unique_value($value, &$target_array) {    if(!in_array($value, $target_array, true))        $target_array[] = $value;}array_walk($merged_values, 'unique_value', $unique_values);

I think one can assume that the internal loops (i.e. what array_walk is doing) are at least not slower than explicit loops.

array_unique(array_merge($arr[0], $arr[1]));

or for an unlimited case, I think this should work:

$result_arr = array();foreach ($arr as $sub_arr) $result_arr = array_merge($result_arr, $sub_arr);$result_arr = array_unique($result_arr);