golang中map类型的排序方法

我们知道，在golang中map类型的键值key/value都是无序排列的，这篇博客讨论一部分我在学习语法过程中思考的排序的方法

---

这里我们考虑下面这种map如何按照数字大小排序输出？

	map1["Mon"]=1
	map1["Tue"]=2
	map1["Wed"]=3
	map1["Thu"]=4
	map1["Fri"]=5
	map1["Sat"]=6
	map1["Sun"]=7

首先将key/value拷贝进一个切片，对切片调用sort包进行排序
教程中采用的是map[string]int类型，将string进行字母排序后输出即可
我们思考一下：如果是对int进行排序呢？我们将int赋值给一个切片value
以一个星期每天为例：

//拷贝到切片后排序结果
value[0]=1
value[1]=2
value[2]=3
......
//但是将int排序后很难再去map中找其对应的string

但是将int排序后很难再去map中找其对应的string，就好比我们知道数组每一个位置对应的数值，但是知道这个数值难以反推回对应是第几个数对吧？

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于是再循环一次map，判断哪个string对应按顺序排列的int（多一次循环&判断）

package main
import "fmt"
import "sort"

func main() {
	map1 := make(map[string]int)
	map1["Mon"]=1
	map1["Tue"]=2
	map1["Wed"]=3
	map1["Thu"]=4
	map1["Fri"]=5
	map1["Sat"]=6
	map1["Sun"]=7
	fmt.Println("unsorted:")
	for key,val := range map1{
		fmt.Printf("%s is the %d of a week\n",key,val)
	}
	fmt.Println("sorted:")
	value := make([]int,len(map1))
	i := 0
	for _,val := range map1{
		value[i]=val
		i++
	}
	sort.Ints(value)
	for i,_ := range value{
		for j := range map1{
			if map1[j]== value[i]{
				fmt.Printf("%s is the %d of a week\n",j,value[i])			
			}
		}
	}
} 

output：

unsorted:
Wed is the 3 of a week
Thu is the 4 of a week
Fri is the 5 of a week
Sat is the 6 of a week
Sun is the 7 of a week
Mon is the 1 of a week
Tue is the 2 of a week
sorted:
Mon is the 1 of a week
Tue is the 2 of a week
Wed is the 3 of a week
Thu is the 4 of a week
Fri is the 5 of a week
Sat is the 6 of a week
Sun is the 7 of a week

这样双重循环加判断是个方法，我们也可以采用另一种方法：先交换键值，然后排序！

package main
import "fmt"

func main() {
	map1 := make(map[string]int)
	map1["Mon"]=1
	map1["Tue"]=2
	map1["Wed"]=3
	map1["Thu"]=4
	map1["Fri"]=5
	map1["Sat"]=6
	map1["Sun"]=7
	invMap := make(map[int]string,len(map1))
	for k,v := range map1{
		invMap[v]=k
	}
	fmt.Println("inverted:")
	for k,v := range invMap{
		fmt.Printf("The %d day is %s\n",k,v)
	}
} 

当然这个时候发现，我们再用map对key排序方法对数字进行排序，输出对应字符串也就非常方便了！

package main
import "fmt"
import "sort"

func main() {
	map1 := make(map[string]int)
	map1["Mon"]=1
	map1["Tue"]=2
	map1["Wed"]=3
	map1["Thu"]=4
	map1["Fri"]=5
	map1["Sat"]=6
	map1["Sun"]=7
	invMap := make(map[int]string,len(map1))
	for k,v := range map1{
		invMap[v]=k
	}
	fmt.Println("inverted:")
	for k,v := range invMap{
		fmt.Printf("The %d day is %s\n",k,v)
	}
	fmt.Println("inverted and sorted:")

	value := make([]int,len(invMap))
	i := 0
	for val,_ := range invMap{
		value[i]=val
		i++
	}
	sort.Ints(value)
	for _,j := range value{
		fmt.Printf("The %d day is %s\n",j,invMap[j])
	}
} 

output:

inverted:
The 6 day is Sat
The 7 day is Sun
The 1 day is Mon
The 2 day is Tue
The 3 day is Wed
The 4 day is Thu
The 5 day is Fri
inverted and sorted:
The 1 day is Mon
The 2 day is Tue
The 3 day is Wed
The 4 day is Thu
The 5 day is Fri
The 6 day is Sat
The 7 day is Sun

这样也就实现了对数字的排序⭐Bingo！