合并具有相同列值的二维数组行并对另一列求和[重复]

我有一个像这样的二维数组：像这样：

[
    ['city' => 'NewYork', 'cash' => 1000],
    ['city' => 'Philadelphia', 'cash' => 2300],
    ['city' => 'NewYork', 'cash' => 2000]
]

我想对值进行求和cash共享相同的行city值以形成具有相同二维结构的结果。

期望的结果：

[
    ['city' => 'NewYork', 'cash' => 3000],
    ['city' => 'Philadelphia', 'cash' => 2300],
]

使用功能array_reduce() http://php.net/manual/en/function.array-reduce.php合并具有相同的项目city:

$input = array(
    array('city' => 'NewYork',      'cash' => '1000'),
    array('city' => 'Philadelphia', 'cash' => '2300'),
    array('city' => 'NewYork',      'cash' => '2000'),
);

$output = array_reduce(
    // Process the input list
    $input,
    // Add each $item from $input to $carry (partial results)
    function (array $carry, array $item) {
        $city = $item['city'];
        // Check if this city already exists in the partial results list
        if (array_key_exists($city, $carry)) {
            // Update the existing item
            $carry[$city]['cash'] += $item['cash'];
        } else {
            // Create a new item, index by city
            $carry[$city] = $item;
        }
        // Always return the updated partial result
        return $carry;
    },
    // Start with an empty list
    array()
);