print_r($array); Array ( [0] => Array ( [name] => yamada [blood] => A ) [1] => Array ( [name] => tanaka [blood] => B ) [2] => Array ( [name] => sato [blood] => A ) [3] => Array ( [name] => kato [blood] => O ) )
$array2 = array_column($array, "blood") ; print_r($array2);
Array ( [0] => A [1] => B [2] => A [3] => O )
$array3 = array_unique($array2); print_r($array3);
Array ( [0] => A [1] => B [3] => O )
$array4 = array_values($array3); print_r($array4);
Array ( [0] => A [1] => B [2] => O )
arsort($array4) ; // 逆順ソート print_r($array4) ;
Array ( [2] => O [1] => B [0] => A )