Compare two multidimensional array and replace values based on matching keys - php

Question

I have 2 arrays of different length:
$array1 = Array
(
[0] => Array
(
['_id'] => "Group1"
['M'] => 0
['F'] => 0
)
[1] => Array
(
['_id'] => "Group2"
['M'] => 0
['F'] => 0
)
[2] => Array
(
['_id'] => "Group3"
['M'] => 0
['F'] => 0
)
[3] => Array
(
['_id'] => "Group4"
['M'] => 0
['F'] => 0
)
)
$array2 = Array
(
[0] => Array
(
['_id'] => "Group2"
['M'] => 180
['F'] => 200
)
[1] => Array
(
['_id'] => "Group4"
['M'] => 360
['F'] => 500
)
)
I want to compare the values of ['_id'] in both array and if they match, I will replace the values of ['M'] and ['F'] in array1 with those from array2 based on the corresponding ['_id].
So my desired ouptput would be:
$array1 = Array
(
[0] => Array
(
['_id'] => "Group1"
['M'] => 0
['F'] => 0
)
[1] => Array
(
['_id'] => "Group2"
['M'] => 180
['F'] => 200
)
[2] => Array
(
['_id'] => "Group3"
['M'] => 360
['F'] => 500
)
[3] => Array
(
['_id'] => "Group4"
['M'] => 0
['F'] => 0
)
)
This is my code but I can't seem to get the values replaced with the new values. The values are still the same as before.
foreach ($array1 as $defArr)
{
foreach ($array2 as $dayArr)
{
if($dayArr['_id'] == $defArr['_id'])
{
$defArr['M'] = $dayArr['M'];
$defArr['F'] = $dayArr['F'];
}
}
}

Answer 1

This can be a one-character change:
foreach ($array1 as $defArr)
goes to
foreach ($array1 as &$defArr)
# ^
The & reference operator points to the original sub array in the foreach loop context rather than a temporary variable.
However, it's a bit safer to use the index explicitly:
foreach ($array1 as $i => $defArr) {
foreach ($array2 as $j => $dayArr) {
if ($dayArr['_id'] == $defArr['_id']) {
$array1[$i]['M'] = $array2[$j]['M'];
$array1[$i]['F'] = $array2[$j]['F'];
}
}
}
If speed is important or $array2 is large, the time complexity of your algorithm is O(n * m). I recommend hashing $array2 for fast lookups as follows (O(n)):
$lookup = array_reduce($array2, function ($a, $e) {
$a[$e['_id']] = $e;
return $a;
});
foreach ($array1 as $i => $e) {
if (array_key_exists($e['_id'], $lookup)) {
$array1[$i]['M'] = $lookup[$e['_id']]['M'];
$array1[$i]['F'] = $lookup[$e['_id']]['F'];
}
}
Try it!

Answer 2

<?php
$array1 = [['_id'=>'abc','M'=>0,'F'=>0],['_id'=>'abcd','M'=>0,'F'=>0],['_id'=>'abcde','M'=>0,'F'=>0]];
$array2 = [['_id'=>'abc','M'=>50,'F'=>300],['_id'=>'abcde','M'=>600,'F'=>700]];
foreach($array2 as $key=> $array2value){
$searched_in_array_1= array_search($array2value['_id'],array_column($array1,'_id'));
if(is_numeric($searched_in_array_1)) $array1[$searched_in_array_1] = $array2value;
}
var_dump($array1);
?>
You want to get a help with php array functions when dealing with arrays. I have used array_column and array_search functions for this