How to multiply numeric array values of similar keys in Php?

Question

   $a = array ('x' => 2, 'y' => 3);
   $b = array (          'y' => 2, 'z' => 3);

// $c = $a * $b;
// i would like to have

// $c = array ('x' => 0, 'y' => 6, 'z' => 0);

Answer 1

If you want to multiply any similar keys together, you will need to get a list of the keys. array_keys would appear to be just the function for that.

function foo($a, $b)
{
   foreach(array_keys($a) as $i)
   {
      if(array_key_exists($i, $b){  // exists in a and b
          $result[$i] = $a[$i]*$b[$i];
      }else{  // exists and a but not b
          $result[$i] = 0;
      }
   }
   foreach(array_keys($b) as $i)
   {
      if(not array_key_exists($i, $a){ //exists in b but not i a
          $result[$i] = 0;
      }
   }
   return $result
}

This will (hopefully) work for any set of keys you hand in, not just x, y, and z.

Answer 2

You could use array_map and abuse bcmul for this purpose:

array_map( 'bcmul', $a, $b ) == $a * $b

Answer 3

You'll have to use a library or define the cross product yourself:

function cross_product($a, $b)
{
  return array( $a['y'] * $b['z'] - $a['z'] * $b['y'], ...
}

http://en.wikipedia.org/wiki/Cross_product

After further examination of what you're doing, it looks as though you'd like something along the lines of:

function multiply_arr($a, $b)
{
  return array($a['x'] * $b['x'], $a['y'] * $b['y'], $a['z'] * $b['z]);
}

again, you'll have to make your own function, and you ought to do some error checking in case a value is undefined.

Answer 4

3D Captcha has got what you are looking for. You may need to do some error checking on it though.