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<?php function flatten($array, $prefix = '') { $return = []; foreach ($array as $key => $value) { if (is_array($value)) { $return = array_merge($return, flatten($value, $prefix . $key . '_')); } else { $return[$prefix . $key] = $value; } } return $return; } // proof that it's working on the simple cases var_dump(flatten([ 1, 2, 3 => [4, 5] ])); var_dump(flatten([ [1, 2], [3, 4] ])); // use array_values on the result if you don't care about keys // simple multidimensional array var_dump(flatten([ 'a' => [ 'b' => 'value', ] ])); // proof that it's not overwriting values like all the other solutions var_dump(flatten([ 'a' => [ 'b' => 'value', ], 'c' => [ 'b' => 'anothervalue', ], ]));