如何在Groovy中使用多个groupBy和max

在Groovy中，我们可以使用多个groupBy和max函数来实现对数据集进行多重分组和获取最大值的操作。

首先，groupBy函数可以用于对数据集按照指定的属性进行分组。我们可以使用collect方法结合groupBy函数来实现多个groupBy的效果。下面是一个示例代码：

def data = [
    [name: "Alice", age: 25, city: "Beijing"],
    [name: "Bob", age: 30, city: "Shanghai"],
    [name: "Alice", age: 35, city: "Beijing"],
    [name: "Bob", age: 40, city: "Shanghai"],
    [name: "Alice", age: 45, city: "Beijing"]
]

def result = data.groupBy { it.name }.collectEntries { k, v ->
    [k, v.groupBy { it.city }]
}

println result

上述代码将根据姓名和城市对数据进行分组，并输出结果：

[
    Alice: [
        Beijing: [
            [name: Alice, age: 25, city: Beijing],
            [name: Alice, age: 35, city: Beijing],
            [name: Alice, age: 45, city: Beijing]
        ]
    ],
    Bob: [
        Shanghai: [
            [name: Bob, age: 30, city: Shanghai],
            [name: Bob, age: 40, city: Shanghai]
        ]
    ]
]

接下来，我们可以使用max函数来获取每个分组中的最大值。再次利用collect方法，可以实现对多个分组的最大值获取。以下是示例代码：

def data = [
    [name: "Alice", age: 25, city: "Beijing"],
    [name: "Bob", age: 30, city: "Shanghai"],
    [name: "Alice", age: 35, city: "Beijing"],
    [name: "Bob", age: 40, city: "Shanghai"],
    [name: "Alice", age: 45, city: "Beijing"]
]

def result = data.groupBy { it.name }.collectEntries { k, v ->
    [k, v.groupBy { it.city }.collectEntries { k2, v2 ->
        [k2, v2.max { it.age }]
    }]
}

println result

上述代码将获取每个姓名分组中每个城市分组的年龄最大值，并输出结果：

[
    Alice: [
        Beijing: [name: Alice, age: 45, city: Beijing]
    ],
    Bob: [
        Shanghai: [name: Bob, age: 40, city: Shanghai]
    ]
]

通过以上示例代码，我们可以在Groovy中使用多个groupBy和max函数实现多重分组和获取最大值的操作。在实际应用中，可以根据具体需求进行适当的修改和扩展。