Php 如何使用group by对数组进行计数

我有一个数组

Array
(
    [0] => stdClass Object
        (
            [id] => 226
            [city] => Dhaka
        )

    [1] => stdClass Object
        (
            [id] => 228
            [city] => Charleston County
        )

    [2] => stdClass Object
        (
            [id] => 229
            [city] => Dhaka
        )

    [3] => stdClass Object
        (
            [id] => 232
            [city] => Dhaka
        )

    [4] => stdClass Object
        (
            [id] => 234
            [city] => Miami-Dade County
        )

来达卡三次

所以我希望我的结果是达卡=3，迈阿密戴德郡=1，查尔斯顿郡=1

这是一个示例数组，所有数据都将动态出现

PHP>=5.3.0：

$result = array_count_values(array_map(function($v) {
                                           return $v->city;
                                       }, $array));

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对于早期版本，为什么？您需要构建一个数组映射函数，或者在数组中循环，并构建一个一维函数进行计数。

您可以在数组上循环，并在运行时对每个城市的实例进行计数

$city_counts = array();                            // create an array to hold the counts
foreach ($array as $city_object) {                 // loop over the array of city objects
// checking isset will prevent undefined index notices    
if (isset($city_counts[$city_object->city])) {            
        $city_counts[$city_object->city]++;        // increment the count for the city
    } else {
        $city_counts[$city_object->city] = 1;      // initialize the count for the city
    }
}

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请告诉我们你试过了，告诉我们你的php代码。这听起来非常类似于这篇文章没有问题。真可惜，不会的。这是一个非常方便的功能。