How to count the number of occurrences of a specific subscript in a 2D array in PHP?

Efficiently count the number of occurrences of specific subscript values ​​in PHP two-dimensional arrays

This article introduces an efficient method to count the number of occurrences of a specific subscript value in a PHP two-dimensional array. Suppose we have a two-dimensional array, each subarray contains three key-value pairs, id , name and age , and we need to count the number of elements with age value of 18.

Here is an example two-dimensional array:

 $array = [
    ['id' => 1, 'name' => 'A', 'age' => 19],
    ['id' => 2, 'name' => 'B', 'age' => 20],
    ['id' => 3, 'name' => 'C', 'age' => 18],
    ['id' => 5, 'name' => 'D', 'age' => 18],
    ['id' => 6, 'name' => 'E', 'age' => 18]
];

We can use the array_reduce function to implement statistics concisely:

 $count = array_reduce($array, function ($carry, $item) {
    return $item['age'] === 18 ? $carry : $carry;
}, 0);

echo "There are {$count} elements with age of 18."; // Output: There are 3 elements with age of 18.

The array_reduce function passes each element in the array $array to the anonymous function in turn. The anonymous function checks whether age is equal to 18, and if so, the accumulator $carry is added to 1; otherwise, $carry remains unchanged. The initial value is 0. Finally, array_reduce returns the value of the accumulator, that is, the number of elements with age of 18.

This approach is simpler and more efficient than using foreach loops, especially when dealing with large arrays, with more obvious performance advantages. You can modify $item['age'] === 18 part to count the values ​​of other subscripts as needed. For example, to count the number of elements with id 3, just modify the part to $item['id'] === 3 .

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