How to count the number of specific key-value pairs in a PHP 2D array?

Detailed explanation of the method of efficiently counting the number of specific key-value pairs in PHP two-dimensional arrays

This article will introduce how to efficiently count the number of specific key-value pairs in a PHP two-dimensional array. Suppose you have a two-dimensional array that needs to count the number of elements in which a specific key's value is equal to a specific value.

Question description:

Given a PHP two-dimensional array, for example:

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

We need to count the number of elements with age value of 18.

Solution:

You can loop through the array using foreach and count using conditional statements:

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

$count = 0;
foreach ($arr as $item) {
    if (isset($item['age']) && $item['age'] == 18) {
        $count ;
    }
}

echo "Number of elements with Age of 18: " . $count; // Output: Number of elements with Age of 18: 2

This code first initializes the counter $count to 0. It then iterates over each element in the array. isset($item['age']) checks whether age key exists to avoid errors with undefined indexes. If the age key exists and the value is 18, the counter $count is incremented by 1. Finally, it outputs statistics.

More advanced solutions (using array_filter and count ):

For more complex statistical requirements, you can use array_filter function and count function combination:

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

$filtered = array_filter($arr, function ($item) {
    return isset($item['age']) && $item['age'] == 18;
});

$count = count($filtered);

echo "Number of elements with Age of 18: " . $count; // Output: Number of elements with Age of 18: 2

The array_filter function uses an anonymous function as a callback to filter out elements that meet the conditions ( age value is 18). The count function directly calculates the number of elements in the filtered array. This method is simpler and has better readability. Which method to choose depends on your personal preferences and code style, and both methods can achieve the same effect.

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