Java, Go 实现map针对某个字段进行group by

其实这个问题可以简化成实现 wordcount 功能。

一、Java案例，对数组字符实现 wordcount：

String[] a = {"a","b","c","d","a","b","a","c","e"};

Map<String, Integer> map = new HashMap<String, Integer>();
for (int i = 0; i < arrays.length; i++) {
    if (map.get(arrays[i]) != null) {
        map.put(arrays[i], map.get(arrays[i]) + 1);
    } else {
        map.put(arrays[i], 1);
    }
}

Set<String> keys = map.keySet();
for (String key: keys) {
    Integer value = map.get(key);
    System.out.println("元素" + key + " " + value);
}

二、Go案例，需要对 Slice里面的 UID字段进行word count，然后把word count写入到对应的ExtInfo字段

 

type MyStruct struct {
   UID int
   ExtInfo map[string]int
}

var slice = []*MyStruct{
   {
      UID: 1,
      ExtInfo: make(map[string]int),
   },
   {
      UID: 1,
      ExtInfo: make(map[string]int),
   },
   {
      UID: 2,
      ExtInfo: make(map[string]int),
   },
   {
      UID: 1,
      ExtInfo: make(map[string]int),
   },
}

 

 

 1、word count，参考Java案例实现的word count原理

map1 := make(map[int]int)
for _, v := range slice {
   if _, ok := map1[v.UID]; ok {
      map1[v.UID] = map1[v.UID] + 1
   } else {
      map1[v.UID] = 1
   }
}

fmt.Println(map1)

2、将 word count写入到对应的ExtInfo字段

map2 := make(map[int]*MyStruct)
for _, v := range slice {
   if _, ok := map1[v.UID]; ok {
      v.ExtInfo["count"] = map1[v.UID]
      map2[v.UID] = v
   }
}
fmt.Println(map2)