PHP 配列を複数のフィールドでグループ化する方法の詳細な説明

$data = [
    ['name' => 'John', 'city' => 'New York'],
    ['name' => 'Jane', 'city' => 'London'],
    ['name' => 'Bob', 'city' => 'New York'],
];

// 按城市分组
$grouped = array_column($data, 'city');

// 输出结果
print_r($grouped);

[
    'New York' => [
        ['name' => 'John', 'city' => 'New York'],
        ['name' => 'Bob', 'city' => 'New York'],
    ],
    'London' => [
        ['name' => 'Jane', 'city' => 'London'],
    ],
]

$data = [
    ['name' => 'John', 'city' => 'New York', 'age' => 25],
    ['name' => 'Jane', 'city' => 'London', 'age' => 30],
    ['name' => 'Bob', 'city' => 'New York', 'age' => 28],
];

// 按城市和年龄分组
array_multisort(array_column($data, 'city'), SORT_ASC, array_column($data, 'age'), SORT_ASC, $data);

// 输出结果
print_r($data);

[
    ['name' => 'John', 'city' => 'New York', 'age' => 25],
    ['name' => 'Bob', 'city' => 'New York', 'age' => 28],
    ['name' => 'Jane', 'city' => 'London', 'age' => 30],
]

function group_by_fields(array $data, array $fields)
{
    $grouped = [];
    foreach ($data as $row) {
        $key = '';
        foreach ($fields as $field) {
            $key .= $row[$field] . ',';
        }
        $key = trim($key, ',');
        $grouped[$key][] = $row;
    }
    return $grouped;
}

$data = [
    ['name' => 'John', 'city' => 'New York', 'age' => 25],
    ['name' => 'Jane', 'city' => 'London', 'age' => 30],
    ['name' => 'Bob', 'city' => 'New York', 'age' => 28],
];

// 按城市和年龄分组
$grouped = group_by_fields($data, ['city', 'age']);

// 输出结果
print_r($grouped);

[
    'New York,25' => [['name' => 'John', 'city' => 'New York', 'age' => 25]],
    'New York,28' => [['name' => 'Bob', 'city' => 'New York', 'age' => 28]],
    'London,30' => [['name' => 'Jane', 'city' => 'London', 'age' => 30]],
]