PHP Array - id's unite and sort by year-CodePudding

I have array $arr :

Array ( [0] => Array ( [id] => 1 [year] => 1999 ) [1] => Array ( [id] => 1 [year] => 2022 ) [2] => Array ( [id] => 2 [year] => 2020 ) [3] => Array ( [id] => 1 [year] => 2020 ) )

and I want to unite equal years and sort ids like that:

"2022" : "1"
"2020" : "1", "2"
"1999" : "1"

How can I do it??? Thanks!

CodePudding user response：

I factored a simple function that takes your array as input and will return a new array grouped by year. Such function just relies on foreach statements without playing too far with callbacks/closures and functional programming.

I included a live example that will show the var_dump of the grouped variable:

https://sandbox.onlinephpfunctions.com/c/20e1f

  <?php
    
    //input
    $items = [
      ['id' => 1, 'year' => 1999],
      ['id' => 1, 'year' => 2022],
      ['id' => 2, 'year' => 2020],
      ['id' => 1, 'year' => 2020]
    ];
    
    $grouped = groupItems($items);
    var_dump($grouped);
    
    /**
     * Takes your input array as argument
     * and returns its items grouped by year
     */
    function groupItems($input){
        $groupedByYear = [];
        //foreach item in input as item
        foreach($input as $item)
        { 
          //if the grouped array still doesn't contain this year
          if (!array_key_exists($item['year'], $groupedByYear))
            //initialize an empty array for this year as a new group
            $groupedByYear[$item['year']] = [];
          //add this item id to the year group
          $groupedByYear[$item['year']][] = $item['id'];
        }
        //sort children
        foreach($groupedByYear as $key => &$value){
            sort($value);
        }
        return $groupedByYear;
    }