How to group and count arrays according to specified rules in PHP

How to group and count arrays according to specified rules in PHP

In PHP development, we often encounter situations where we need to group and count arrays. Whether it is counting the number of occurrences of a certain element or grouping according to a certain field, you can use the array functions provided by PHP to achieve it. Two common group counting methods will be introduced below, with code examples attached.

1. Count the number of occurrences of elements in an array

When we need to count the number of occurrences of each element in an array, we can use the array functionarray_count_values(). This function returns an associative array, where the keys represent the elements in the array and the values ​​represent the number of times the element appears in the array.

The following is a sample code:

$array = [1, 2, 1, 3, 4, 2, 1];

$counts = array_count_values($array);

// 输出统计结果
foreach ($counts as $key => $value) {
    echo $key . '：' . $value . '次<br>';
}

The running results are as follows:

1：3次
2：2次
3：1次
4：1次

2. Group and count the arrays according to the specified fields

Suppose we have an array of students, each student has name and age fields. We need to group students according to their age and count the number of students in each age group. This can be achieved using the array_reduce() function and anonymous function.

The following is a sample code:

$students = [
    ['name' => 'Alice', 'age' => 18],
    ['name' => 'Bob', 'age' => 20],
    ['name' => 'Cindy', 'age' => 18],
    ['name' => 'David', 'age' => 20],
    ['name' => 'Emily', 'age' => 22],
];

$groupedStudents = array_reduce($students, function ($result, $student) {
    $age = $student['age'];
    if (!isset($result[$age])) {
        $result[$age] = 0;
    }
    $result[$age]++;
    return $result;
}, []);

// 输出分组结果
foreach ($groupedStudents as $age => $count) {
    echo $age . '岁的学生有' . $count . '人<br>';
}

The running results are as follows:

18岁的学生有2人
20岁的学生有2人
22岁的学生有1人

Through the above sample code, we can implement the grouping and counting functions of arrays in PHP. Whether it is counting the number of occurrences of elements in an array, or grouping and counting arrays according to specified fields, you can use the functions provided by PHP to complete it. These functions are very useful in data analysis, statistics and business logic processing. I hope the above examples can help you better understand and apply the group counting function of PHP arrays.

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