19、map groupBy分组

class GroovyTest {

    static void main(args) {

        println([
                [name:'Clark',city:'London'],
                [name:'Sharma',city:'London'],
                [name:'Maradona',city:'LA'],
                [name:'Zhang',city:'HK'],
                [name:'Ali',city:'HK'],
                [name:'Liu',city:'HK']
        ].groupBy{it.city})

    }
}

输出：

[London:[[name:Clark, city:London], [name:Sharma, city:London]], LA:[[name:Maradona, city:LA]], HK:[[name:Zhang, city:HK], [name:Ali, city:HK], [name:Liu, city:HK]]]