問題描述

給定二維陣列，依特定鍵（如 group_id）分組，數值欄位求和：

$data = [
    ['group_id' => 13, 'team_price' => 88.00, 'satopay_price' => 85.00, 'quantity' => 5],
    ['group_id' => 13, 'team_price' => 12.00, 'satopay_price' => 11.00, 'quantity' => 3],
    ['group_id' => 14, 'team_price' => 4.99,  'satopay_price' => 4.60,  'quantity' => 1],
    ['group_id' => 14, 'team_price' => 12.00, 'satopay_price' => 11.00, 'quantity' => 2],
    ['group_id' => 15, 'team_price' => 13.00, 'satopay_price' => 11.00, 'quantity' => 2],
];

自訂函數實作

function groupSum(array $row, array &$result, string $groupKey): void {
    // 尋找現有分組
    $foundIdx = null;
    foreach ($result as $idx => $group) {
        if ($group[$groupKey] === $row[$groupKey]) {
            $foundIdx = $idx;
            break;
        }
    }
    
    if ($foundIdx !== null) {
        // 既有分組：數值欄位累加
        foreach ($row as $key => $value) {
            if ($key !== $groupKey && is_numeric($value)) {
                $result[$foundIdx][$key] += $value;
            }
        }
    } else {
        // 新分組：直接加入
        $result[] = $row;
    }
}

$result = [];
foreach ($data as $row) {
    groupSum($row, $result, 'group_id');
}
print_r($result);

結果

[
    ['group_id' => 13, 'team_price' => 100.00, 'satopay_price' => 96.00, 'quantity' => 8],
    ['group_id' => 14, 'team_price' => 16.99,  'satopay_price' => 15.60, 'quantity' => 3],
    ['group_id' => 15, 'team_price' => 13.00,  'satopay_price' => 11.00, 'quantity' => 2],
]

優化版：使用鍵名索引 O(1) 查找

function groupSumOptimized(array $row, array &$result, string $groupKey): void {
    $groupVal = $row[$groupKey];
    if (!isset($result[$groupVal])) {
        $result[$groupVal] = $row;
        return;
    }
    foreach ($row as $key => $value) {
        if ($key !== $groupKey && is_numeric($value)) {
            $result[$groupVal][$key] += $value;
        }
    }
}

// 使用時以 group_id 為索引
$result = [];
foreach ($data as $row) {
    groupSumOptimized($row, $result, 'group_id');
}
// 如需連續索引：$result = array_values($result);

資料庫層面替代方案

若資料源自資料庫，優先用 SQL 分組：

SELECT group_id, 
       SUM(team_price) as team_price,
       SUM(satopay_price) as satopay_price,
       SUM(quantity) as quantity
FROM orders
GROUP BY group_id

資料庫引擎優化程度遠高於 PHP 迴圈，大量資料務必下推至 SQL 層處理。