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Maico Orazio
Maico Orazio

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Using array_merge in a PHP loop is considered bad practice

#php #loop #performance

To use the array_merge function in a for / foreach / while loop, do the following:

$arraysToMerge = [ [1, 2], [2, 3], [5, 8] ]; $arraysMerged = []; foreach($arraysToMerge as $array) { $arraysMerged = array_merge($arraysMerged, $array); }
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is a poor practice 😱 because it is a performance drain (especially on memory).

Since PHP 5.6, there is a new operator, the spread operator,

$arraysToMerge = [ [1, 2], [2, 3], [5,8] ]; $arraysMerged = array_merge([], ...$arraysToMerge); print_r($arraysMerged);
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output

Array ( [0] => 1 [1] => 2 [2] => 2 [3] => 3 [4] => 5 [5] => 8 )
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which automatically expands the array without the need to loop through it.

  • No more performance issues
  • No for / foreach / while loops
  • Processed in a single line of code.

A more complex example can be represented by the following case:

  • I have a list of students
  • For each of them, I need to retrieve their used books
  • I need to store them in a new array structure

It is possible to use the spread operator, but an intermediate process is required:

// student data model $students = [['id'=>1],['id'=>2],['id'=>3]]; // retrieve used books by student ID function searchUsedBooksByStudent($id) { $books = []; $books[1] = ['italian', 'history']; $books[2] = ['mathematics']; $books[3] = ['latin']; if (isset($books[$id])) { return $books[$id]; } return []; } $arrayUsedBooks = []; foreach ($students as $student) { $books = searchUsedBooksByStudent($student['id']); if ($books) { $arrayUsedBooks[] = $books; } } $arraysMerged = array_merge([], ...$arrayUsedBooks); print_r($arraysMerged);
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output

 Array ( [0] => italian [1] => history [2] => mathematics [3] => latin )
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I hope these examples are helpful. Now, look at your code to see what you can improve!

Good work 👨‍💻

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