更好的方法来编写嵌套的foreach循环，多个数组比较php

Question

I have 2 multidimensional arrays. I run the first one through a foreach loop to gain data from it. then run the second foreach loop inside the first creating a nested foreach loop.then inside the second foreach loop I run an if statement to compare a value from the first array to the second array and display some output which works, however I am a little concerned about long run-time. so my question is, is there a cleaner, neater way to write it with a shorter run type:

@foreach($arrayOne as $firstArray)
    @foreach($arrayTwo as $secondArray)
        @if($firstArray['id'] == $secondArray['linkedId'])
            /*output some data*/
        @endif
    @endforeach      
@endforeach

Answer 1

The complexity of two-nested-foreach solution is O(n * k), where n = len(array1) and k = len(array2). However you can achieve a smaller complexity O(n + k) via using hash tables (assoc arrays in PHP world).

$twoByLinkedId = [];
foreach ($arrayTwo as $x) {  // K iterations
    if (empty($twoByLinkedId[$x['linkedId']])) {
        $twoByLinkedId[$x['linkedId']] = [];
    }
    array_push($twoByLinkedId[$x['linkedId']], $x);
}

foreach ($arrayOne as $el) {  // N iterations
    $entries = empty($twoByLinkedId[$el['id']]) 
        ? [] 
        : $twoByLinkedId[$el['id']];
    foreach ($entries as $entry) {  // only few iterations
        /* output $entry */
    }
}

So you can see that the complexity of the solution is O(k + n*t), where t is a a small number.

Of course, the trick makes sense only if the lengths of both arrays are really big, otherwise simple nested foreach is a good solution too.