合并具有相同列值的2d数组行，并对另一列求和

使用函数array_reduce()组合具有相同city:的项目

$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()
);

使用任何一个以上的循环（或循环函数）来求和值是低效的。

这里有一个方法，它使用临时键来构建结果数组，然后在循环结束后重新索引结果数组。

代码：（Demo）由于"；零合并运算符"；

foreach ($array as $row) {
    $result[$row['city']] = [
        'city' => $row['city'],
        'cash' => ($result[$row['city']]['cash'] ?? 0) + $row['cash']
    ];
}
var_export(array_values($result));

代码：（Demo）带有引用，以避免声明一级分组密钥和任何全局范围的变量

var_export(
    array_reduce(
        $array,
        function($result, $row) {
            static $ref;
            if (!isset($ref[$row['city']])) {
                $ref[$row['city']] = $row;
                $result[] = &$ref[$row['city']];
            } else {
                $ref[$row['city']]['cash'] += $row['cash'];
            }
            return $result;
        }
    )
);

代码：（演示）

foreach ($array as $a) {
    if (!isset($result[$a['city']])) {
        $result[$a['city']] = $a;  // store temporary city-keyed result array (avoid Notices)
    } else {
        $result[$a['city']]['cash'] += $a['cash'];  // add current value to previous value
    }
}
var_export(array_values($result));  // remove temporary keys

尝试以下代码：

<?php
$arr = array(
        array('city' => 'NewYork', 'cash' => '1000'),
        array('city' => 'Philadelphia', 'cash' => '2300'),
        array('city' => 'NewYork', 'cash' => '2000'),
    );
$newarray = array();
foreach($arr as $ar)
{
    foreach($ar as $k => $v)
    {
        if(array_key_exists($v, $newarray))
            $newarray[$v]['cash'] = $newarray[$v]['cash'] + $ar['cash'];
        else if($k == 'city')
            $newarray[$v] = $ar;
    }
}
print_r($newarray);

输出：

Array
(
    [NewYork] => Array
        (
            [city] => NewYork
            [cash] => 3000
        )
    [Philadelphia] => Array
        (
            [city] => Philadelphia
            [cash] => 2300
        )
)

演示：
http://3v4l.org/D8PME

试试这个：

 $sumArray = array();
    foreach ($arrTotal as $k=>$subArray) {
        foreach ($subArray as $id=>$value) {
            $sumArray[$subArray['city']]+=$value;
        }
    }
    var_dump($sumArray);

输出：

array(2) {
  ["NewYork"]=>
  int(3000)
  ["Philadelphia"]=>
  int(2300)
}