Question

Consider the following array as input:

$input = array('A', 'B', 'C', 'D');

I’m looking for a way to make loop though this array, writing down every possible pair of two values. In this example: AB AC AD BC BD CD. Please not that BA doesn’t count as a pair, since AB is already mentioned:

$output = array(
  'A' => 'B',
  'A' => 'C',
  'A' => 'D',
  'B' => 'C',
  'B' => 'D'
);

Any input on how to get this started is appreciated!

Answer 1

$output=array();
for ($i=0;$i<sizeof($input);$i++) {
  $k=$input[$i];
  for ($j=$i+1;$j<sizeof($input);$j++) {
    $v=$input[$j];
    $output[]=array($k=>$v);
  }
}

Edit

As of your comment, the restructured output

$output=array();
//See below
for ($i=0;$i<sizeof($input);$i++) {
  $k=$input[$i];
  $v=array();
  for ($j=$i+1;$j<sizeof($input);$j++) {
    $v[]=$input[$j];
  }
  $output[]=array($k=>$v);
}

This will give you ‘D’=>Array() as a last row, if you don’t want hti you have to change

for ($i=0;$i<sizeof($input);$i++) {

to

for ($i=0;$i<sizeof($input)-1;$i++) {