foreachを使って並び替え

index.php

<?php
$a = array(
  1 => array(1, 0),
  2 => array(2, 1),
  3 => array(3, 1),
  4 => array(4, 1),
  5 => array(5, 0),
  6 => array(6, 0),
  7 => array(7, 0),
  8 => array(8, 5),
  9 => array(9, 5),
);

$b = array();

foreach ($a as $key => $value1) {
//value1の2番目が0だったら処理を通す
  if ($value1[1] == 0) {
    $b[] = $value1;
//valueの1の1番目とvalue2の2番目が一緒だったら処理を通す
    foreach ($a as $key2 => $value2) {
      
      if ($value1[0] == $value2[1]) {
        $b[] = $value2;
      }
    }
  }
}

$a = $b;
print_r($a);

結果

php.php

Array
(
    [0] => Array
        (
            [0] => 1
            [1] => 0
        )

    [1] => Array
        (
            [0] => 2
            [1] => 1
        )

    [2] => Array
        (
            [0] => 3
            [1] => 1
        )

    [3] => Array
        (
            [0] => 4
            [1] => 1
        )

    [4] => Array
        (
            [0] => 5
            [1] => 0
        )

    [5] => Array
        (
            [0] => 8
            [1] => 5
        )

    [6] => Array
        (
            [0] => 9
            [1] => 5
        )

    [7] => Array
        (
            [0] => 6
            [1] => 0
        )

    [8] => Array
        (
            [0] => 7
            [1] => 0
        )

)