How to merge two multi dimensional arrays by key value in php?

Question

I have two arrays

$arr1 = [
    ['month' => 1], 
    ['month' => 2], 
    ['month' => 3], 
    ['month' => 4]
];

$arr2 = [
    ['month' => 3, 'info' => 'Alpha'], 
    ['month' => 4, 'info' => 'Beta']
];

I have tried array_merge & array_merge_recursive both are not merging arrays as my expected.

Expected Merging:

$arr3 = [
    ['month' => 1], 
    ['month' => 2], 
    ['month' => 3, 'info' => 'Alpha'], 
    ['month' => 4, 'info' => 'Beta']
];

Actual with array_merge_recursive is:

$arr3 = array_merge_recursive($arr2, $arr1);

$arr3 = [
    ['month' => 3, 'info' => 'Alpha'], 
    ['month' => 4, 'info' => 'Beta']
    ['month' => 1], 
    ['month' => 2], 
    ['month' => 3], 
    ['month' => 4]
];

Andreas · Answer 1 · 2019-05-21T05:56:26.817

If the arrays are associative on month then you can use array_replace.
First make the arrays associative with array_column then replace $arr1 with $arr2 values.

$arr1 = [
    ['month' => 1], 
    ['month' => 2], 
    ['month' => 3], 
    ['month' => 4]
];

$arr2 = [
    ['month' => 3, 'info' => 'Alpha'], 
    ['month' => 4, 'info' => 'Beta'],
    ['month' => 1, 'info' => 'Gamma'],
];


$arr1 = array_column($arr1, null, 'month');
$arr2 = array_column($arr2, null, 'month');

$result = array_replace($arr1, $arr2);
var_dump($result);

Returns:

array(4) {
  [1]=>
  array(2) {
    ["month"]=>
    int(1)
    ["info"]=>
    string(5) "Gamma"
  }
  [2]=>
  array(1) {
    ["month"]=>
    int(2)
  }
  [3]=>
  array(2) {
    ["month"]=>
    int(3)
    ["info"]=>
    string(5) "Alpha"
  }
  [4]=>
  array(2) {
    ["month"]=>
    int(4)
    ["info"]=>
    string(4) "Beta"
  }
}

https://3v4l.org/tpshB

If you have older version of PHP which does not have array_column then you can use this legacy code from manual

if (!function_exists('array_column')) {
    function array_column($array, $columnKey, $indexKey = null)
    {
        $result = array();
        foreach ($array as $subArray) {
            if (is_null($indexKey) && array_key_exists($columnKey, $subArray)) {
                $result[] = is_object($subArray)?$subArray->$columnKey: $subArray[$columnKey];
            } elseif (array_key_exists($indexKey, $subArray)) {
                if (is_null($columnKey)) {
                    $index = is_object($subArray)?$subArray->$indexKey: $subArray[$indexKey];
                    $result[$index] = $subArray;
                } elseif (array_key_exists($columnKey, $subArray)) {
                    $index = is_object($subArray)?$subArray->$indexKey: $subArray[$indexKey];
                    $result[$index] = is_object($subArray)?$subArray->$columnKey: $subArray[$columnKey];
                }
            }
        }
        return $result;
    }
}

Dear @Andreas, Thanks for your response, unfortunately I have PHP 5.3 on my server. So, I am not able to use array_column. — Karthikeyan Raju, May 21 '19 at 04:59
@KarthikeyanRaju with legacy code from manual it works fine: https://3v4l.org/qEpZW . Array_column is a very handy function to have. — Andreas, May 21 '19 at 06:09
Dear @Andreas, really thanks for your effort towards my question. once again thanks a lot. — Karthikeyan Raju, May 21 '19 at 06:36
@KarthikeyanRaju no problem. I recommend you to implement array_column in your project even if you don't use my answer, it's a very good function to have. — Andreas, May 21 '19 at 09:33

score 0 · Accepted Answer · answered May 20 '19 at 17:57

In this case, I walk the arrays and construct the desired output.

$output = [];
$allMerged = array_merge($arr1, $arr2);
array_walk($allMerged, 
  function($item, $key) use (&$output) {
    print_r($item);
    if ( array_key_exists($item['month'], $output) ) {
        if ( isset($item['info']) ) {
            $output[$item['month']]['info'] = $item['info'];
        } else {
            $output[$item['month']] = $item;
        }
    } else {
        $output[$item['month']] = $item;
    }
});
print_r($output);

Dear @ryantxr, Its worked for me, thanks, I am not able to up vote right answer though I am newly registered user in Stack Overflow. — Karthikeyan Raju, May 21 '19 at 06:35

score -1 · Answer 3 · answered May 20 '19 at 15:38

-1

U can try following code

$newArr = [];
foreach($arr1 as $row) {
    $newArr[$row['month']] = $row;
}
foreach($arr2 as $arr) {
    if(array_key_exists($arr['month'], $newArr)) {
        $newArr[$arr['month']]['info'] = $arr['info'];
    }
} 

print_r($newArr);

answered May 20 '19 at 15:38

Farhad Misirli

187
7

What if `$arr2` had elements that did not exist in `$arr1`? – ryantxr May 20 '19 at 15:46
If u want to add element that doesnt exists in $arr1 U can add it into $newArr using else { $newArr[$arr['month'] = ['month' => $arr['month'] ]; } – Farhad Misirli May 20 '19 at 15:54

How to merge two multi dimensional arrays by key value in php?

3 Answers3