PHP 二维数组按相同的元素分类

原数组 按照group分类

array(8) {

  [0] => array(3) {
    ["id"] => string(1) "1"
    ["tag_name"] => string(3) "公"
    ["group"] => string(1) "1"
  }
  [1] => array(3) {
    ["id"] => string(1) "2"
    ["tag_name"] => string(3) "母"
    ["group"] => string(1) "1"
  }
  [2] => array(3) {
    ["id"] => string(1) "3"
    ["tag_name"] => string(9) "发情期"
    ["group"] => string(1) "2"
  }
  [3] => array(3) {
    ["id"] => string(1) "4"
    ["tag_name"] => string(9) "未成年"
    ["group"] => string(1) "2"
  }
  [4] => array(3) {
    ["id"] => string(1) "5"
    ["tag_name"] => string(6) "绝育"
    ["group"] => string(1) "2"
  }
  [5] => array(3) {
    ["id"] => string(1) "6"
    ["tag_name"] => string(6) "白色"
    ["group"] => string(1) "3"
  }
  [6] => array(3) {
    ["id"] => string(1) "7"
    ["tag_name"] => string(6) "花色"
    ["group"] => string(1) "3"
  }
  [7] => array(3) {
    ["id"] => string(1) "8"
    ["tag_name"] => string(6) "黑色"
    ["group"] => string(1) "3"
  }
}

	foreach ($tags as $v) {
        $res[$v["group"]][] = $v;
     }

把group当做键名 相同的group放入同一个group的数组

array(3) {
  [1] => array(2) {
    [0] => array(3) {
      ["id"] => string(1) "1"
      ["tag_name"] => string(3) "公"
      ["group"] => string(1) "1"
    }
    [1] => array(3) {
      ["id"] => string(1) "2"
      ["tag_name"] => string(3) "母"
      ["group"] => string(1) "1"
    }
  }
  [2] => array(3) {
    [0] => array(3) {
      ["id"] => string(1) "3"
      ["tag_name"] => string(9) "发情期"
      ["group"] => string(1) "2"
    }
    [1] => array(3) {
      ["id"] => string(1) "4"
      ["tag_name"] => string(9) "未成年"
      ["group"] => string(1) "2"
    }
    [2] => array(3) {
      ["id"] => string(1) "5"
      ["tag_name"] => string(6) "绝育"
      ["group"] => string(1) "2"
    }
  }
  [3] => array(3) {
    [0] => array(3) {
      ["id"] => string(1) "6"
      ["tag_name"] => string(6) "白色"
      ["group"] => string(1) "3"
    }
    [1] => array(3) {
      ["id"] => string(1) "7"
      ["tag_name"] => string(6) "花色"
      ["group"] => string(1) "3"
    }
    [2] => array(3) {
      ["id"] => string(1) "8"
      ["tag_name"] => string(6) "黑色"
      ["group"] => string(1) "3"
    }
  }
}