Group array items by key value adding an associative element with the grouped values

Question

Having the following array:

$a = [
    "category" => "Music", 
    "items" => [
        ["ID" => "1", "start_date" => "2018-11-20", "end_date" => "2018-11-28"],
        ["ID" => "2", "start_date" => "2018-11-22", "end_date" => "2018-11-28"],
        ["ID" => "3", "start_date" => "2018-11-26", "end_date" => "2018-11-30"],
        ["ID" => "4", "start_date" => "2018-11-27", "end_date" => "2018-11-31"],
        ["ID" => "4", "start_date" => "2018-11-29", "end_date" => "2018-11-31"]
    ]
];

I would like to 'group' the arrays by end_date but not using end_date as key as I saw in other posts or forums, but by adding the value of end_date as a value of a new key.

So that the expected result would be:

array(
    "category" => "Music",
    "items" => array(
        array(
            "date" => "2018-11-28",
            array("ID" => "1", "start_date" => "2018-11-20", "end_date" => "2018-11-28"),
            array("ID" => "2", "start_date" => "2018-11-22", "end_date" => "2018-11-28"),
        ),
        array(
            "date" => "2018-11-30",
            array("ID" => "3", "start_date" => "2018-11-26", "end_date" => "2018-11-30")
        ),
        array(
            "date" => "2018-11-31",
            array("ID" => "4", "start_date" => "2018-11-27", "end_date" => "2018-11-31"),
            array("ID" => "4", "start_date" => "2018-11-29", "end_date" => "2018-11-31")
        )
    )
);

You have been here long enough to know you should include an attempt. — Andreas, Nov 28 '18 at 16:28
@Andreas: I did linked my attempts (see link to 'forum' and 'posts'). — Nicero, Nov 28 '18 at 16:46
@Omari: because I'm trying to build an API that outputs a JSON which shall be used by a APP that draws it's content associating keys and values. — Nicero, Nov 28 '18 at 16:47

score 2 · Accepted Answer · answered Nov 28 '18 at 16:39

Loop the array and build an temporary associative array with the end date as the key.
Then copy the original array and unset the 'items' and add the new temporary array values.

$a = array("category" => "Music", 
        "items" => array(
            array("ID" => "1", "start_date" => "2018-11-20", "end_date" => "2018-11-28"),
            array("ID" => "2", "start_date" => "2018-11-22", "end_date" => "2018-11-28"),
            array("ID" => "3", "start_date" => "2018-11-26", "end_date" => "2018-11-30"),
            array("ID" => "4", "start_date" => "2018-11-27", "end_date" => "2018-11-31"),
            array("ID" => "4", "start_date" => "2018-11-29", "end_date" => "2018-11-31")
        )
);

foreach($a['items'] as $item){
    $new[$item['end_date']]['date'] = $item['end_date'];
    $new[$item['end_date']][] = $item;
}
$res = $a;
unset($res['items']);
$res['items'] = array_values($new);


var_dump($res);

Output:

array(2) {
  ["category"]=>
  string(5) "Music"
  ["items"]=>
  array(3) {
    [0]=>
    array(3) {
      ["date"]=>
      string(10) "2018-11-28"
      [0]=>
      array(3) {
        ["ID"]=>
        string(1) "1"
        ["start_date"]=>
        string(10) "2018-11-20"
        ["end_date"]=>
        string(10) "2018-11-28"
      }
      [1]=>
      array(3) {
        ["ID"]=>
        string(1) "2"
        ["start_date"]=>
        string(10) "2018-11-22"
        ["end_date"]=>
        string(10) "2018-11-28"
      }
    }
    [1]=>
    array(2) {
      ["date"]=>
      string(10) "2018-11-30"
      [0]=>
      array(3) {
        ["ID"]=>
        string(1) "3"
        ["start_date"]=>
        string(10) "2018-11-26"
        ["end_date"]=>
        string(10) "2018-11-30"
      }
    }
    [2]=>
    array(3) {
      ["date"]=>
      string(10) "2018-11-31"
      [0]=>
      array(3) {
        ["ID"]=>
        string(1) "4"
        ["start_date"]=>
        string(10) "2018-11-27"
        ["end_date"]=>
        string(10) "2018-11-31"
      }
      [1]=>
      array(3) {
        ["ID"]=>
        string(1) "4"
        ["start_date"]=>
        string(10) "2018-11-29"
        ["end_date"]=>
        string(10) "2018-11-31"
      }
    }
  }
}

https://3v4l.org/foKL7

score 0 · Answer 2 · answered Apr 25 '21 at 00:35

You can use functional-style programming to group and re-index the items subarray without declaring any temporary variables in the global space.

As you iterate each row of $array['items'], use temporary keys for grouping and push rows into their respective group. When finished grouping, re-index the data with array_values().

Code: (Demo)

$array = [
    "category" => "Music", 
    "items" => [
        ["ID" => "1", "start_date" => "2018-11-20", "end_date" => "2018-11-28"],
        ["ID" => "2", "start_date" => "2018-11-22", "end_date" => "2018-11-28"],
        ["ID" => "3", "start_date" => "2018-11-26", "end_date" => "2018-11-30"],
        ["ID" => "4", "start_date" => "2018-11-27", "end_date" => "2018-11-31"],
        ["ID" => "4", "start_date" => "2018-11-29", "end_date" => "2018-11-31"]
    ]
];

$array["items"] = array_values(
    array_reduce(
        $array["items"],
        function ($carry, $row) {
            $carry[$row["end_date"]]["data"] = $row["end_date"];
            $carry[$row["end_date"]][] = $row;
            return $carry;
        }
    )
);
var_export($array);

Group array items by key value adding an associative element with the grouped values

2 Answers2