PHP多维数组中如何获取每组tahun和bulan对应的最大pembetulan值

方法1：基础遍历实现（兼容性最好，支持所有PHP版本） #

思路是遍历所有数组元素，以tahun和bulan的组合作为分组标识，每次比对同分组下的pembetulan值，只保留最大值：

<?php
$data = [
  ["tahun" => 2001, "bulan" => 1, "pembetulan" => 0],
  ["tahun" => 2002, "bulan" => 1, "pembetulan" => 0],
  ["tahun" => 2002, "bulan" => 1, "pembetulan" => 1],
  ["tahun" => 2003, "bulan" => 1, "pembetulan" => 0],
  ["tahun" => 2003, "bulan" => 1, "pembetulan" => 1],
  ["tahun" => 2003, "bulan" => 1, "pembetulan" => 2],
  ["tahun" => 2003, "bulan" => 1, "pembetulan" => 3],
  ["tahun" => 2003, "bulan" => 1, "pembetulan" => 4],
  ["tahun" => 2003, "bulan" => 2, "pembetulan" => 0]
];

$groupedMax = [];
foreach ($data as $item) {
    // 用tahun和bulan拼接成分组的唯一key
    $key = $item['tahun'] . '_' . $item['bulan'];
    // 如果当前分组不存在，或者当前值比已存的更大，就更新
    if (!isset($groupedMax[$key]) || $item['pembetulan'] > $groupedMax[$key]['pembetulan']) {
        $groupedMax[$key] = $item;
    }
}
// 可选：去掉临时key，重置为索引数组
$groupedMax = array_values($groupedMax);

// 输出结果
print_r($groupedMax);
?>

输出结果： #

Array
(
    [0] => Array
        (
            [tahun] => 2001
            [bulan] => 1
            [pembetulan] => 0
        )
    [1] => Array
        (
            [tahun] => 2002
            [bulan] => 1
            [pembetulan] => 1
        )
    [2] => Array
        (
            [tahun] => 2003
            [bulan] => 1
            [pembetulan] => 4
        )
    [3] => Array
        (
            [tahun] => 2003
            [bulan] => 2
            [pembetulan] => 0
        )
)

方法2：用array_reduce实现（PHP 5.3+支持） #

如果偏好函数式写法，可以用array_reduce实现同样逻辑，代码更简洁：

$groupedMax = array_values(array_reduce($data, function($carry, $item) {
    $key = $item['tahun'] . '_' . $item['bulan'];
    if (!isset($carry[$key]) || $item['pembetulan'] > $carry[$key]['pembetulan']) {
        $carry[$key] = $item;
    }
    return $carry;
}, []));

两种实现逻辑完全一致，可根据代码风格选择。

内容的提问来源于stack exchange，提问作者Mukhamad Fadil