go map和切片结合使用,map 排序,删除

map和切片结合使用

package main

import(
	"fmt"		
	"math/rand"		
	"time"	
)


func testSliceMap(){
	rand.Seed(time.Now().UnixNano())
	var s []map[string]int
	s = make([]map[string]int, 5, 16)

	for index, val:=range s{
		fmt.Printf("----------slice[%d]=%v\n",index,val)
	}
	// s[0]["stu01"] = 10  // panic: assignment to entry in nil map  必须先对切片中的元素初始化才行

	fmt.Println()
	s[0] = make(map[string]int,16)
	s[0]["stu001"] =1
	s[0]["stu002"] =2
	s[0]["stu003"] =3
	s[0]["stu004"] =4
	for index,val:=range s{
		fmt.Printf("slice[%d]=%v\n",index,val)
	}	
}


func testMapSlice1(){
	rand.Seed(time.Now().UnixNano())
	var s map[string][]int 
	s = make(map[string][]int,16)
	key := "stu01"
	value,ok := s[key]
	if !ok{
		fmt.Println("你好001",s,value,ok)
		s[key]= make([]int,0,16)
		value = s[key]
	}
	fmt.Println("你好002",s,value,ok)
	value = append(value,100)
	fmt.Println("你好003",value)
	value = append(value,200)
	fmt.Println("你好004",value)
	value = append(value,300)
	fmt.Println("你好005",value)
	s[key] = value
	fmt.Printf("map:%v\n",s)
}



func main(){
	testSliceMap()
	testMapSlice1()
}

输出:

----------slice[0]=map[]
----------slice[1]=map[]
----------slice[2]=map[]
----------slice[3]=map[]
----------slice[4]=map[]

slice[0]=map[stu001:1 stu002:2 stu003:3 stu004:4]
slice[1]=map[]
slice[2]=map[]
slice[3]=map[]
slice[4]=map[]
你好001 map[] [] false
你好002 map[stu01:[]] [] false
你好003 [100]
你好004 [100 200]
你好005 [100 200 300]
map:map[stu01:[100 200 300]]

删除,排序

package main

import (
	"fmt"
	"math/rand"
	"sort"
	"time"
)


func testMapSort(){
	rand.Seed(time.Now().UnixNano())
	var a map[string]int = make(map[string]int,1024)

	for i:=0;i<5;i++{
		key:=fmt.Sprintf("stu%d",i)
		value := rand.Intn(100)
		a[key] =value
	}
	fmt.Printf("001 a=%#v\n",a)
	delete(a,"stu3")
	fmt.Printf("002 a=%#v\n",a)

	var keys []string = make([]string, 0, 12)
	for key,value :=range a{
		fmt.Printf("map[%s]=%d\n", key, value)
		keys = append(keys, key)
	}	
	fmt.Printf("keys01  keys:%v\n",keys)

	sort.Strings(keys)
	fmt.Printf("keys02  keys:%v\n",keys)
	for _,value :=range keys{
		fmt.Printf("key:%s val:%d\n",value,a[value])
	}
}


func main(){	
	testMapSort()
}

输出:

001 a=map[string]int{"stu0":82, "stu1":67, "stu2":32, "stu3":76, "stu4":2}
002 a=map[string]int{"stu0":82, "stu1":67, "stu2":32, "stu4":2}
map[stu4]=2
map[stu2]=32
map[stu0]=82
map[stu1]=67
keys01  keys:[stu4 stu2 stu0 stu1]
keys02  keys:[stu0 stu1 stu2 stu4]
key:stu0 val:82
key:stu1 val:67
key:stu2 val:32
key:stu4 val:2

map 未初始化 nil

package main

import(
	"fmt"		
)


func testMap(){
	var a map[string]int
	fmt.Printf("001  a:%#v\n",a)
	// a["stu01"] =100  // 必须先初始化才能赋值否则报错  panic: assignment to entry in nil map 
	if a ==nil{
		a = make(map[string]int ,16)   // map的容量要提前预估下,否则存储不下时会扩容,造成性能消耗
		fmt.Printf("002  a:%#v\n",a)
		if a == nil{
			fmt.Printf("003 实例化了  a:%#v\n",a)
		}else {
			fmt.Printf("004 实例化了  a:%#v\n",a)
		}
		a["stu01"] = 10
		fmt.Printf("a=%#v\n",a)
		a["stu01"] = 11
		a["stu02"] = 12
		a["stu03"] = 13
		a["stu04"] = 14
		a["stu05"] = 15
		fmt.Printf("a=%#v\n",a)
	}
}


// map申明的时候初始化
func testMapInit(){
	var a map[string]int = map[string]int{
		"stu01":11, "stu02":12, "stu03":13, "stu04":14, "stu05":15,
	}
	fmt.Printf("a:%#v\n",a)
	a["stu01"] = 101
	a["stu02"] = 102	
	fmt.Printf("a=%#v\n",a)
	
	var key string ="stu04"
	fmt.Printf("the value of key[%s] is : %d\n",key,a[key])
}


func main(){	
	testMap()
	testMapInit()
}

输出：

001  a:map[string]int(nil)
002  a:map[string]int{}
004 实例化了  a:map[string]int{}
a=map[string]int{"stu01":10}
a=map[string]int{"stu01":11, "stu02":12, "stu03":13, "stu04":14, "stu05":15}
a:map[string]int{"stu01":11, "stu02":12, "stu03":13, "stu04":14, "stu05":15}
a=map[string]int{"stu01":101, "stu02":102, "stu03":13, "stu04":14, "stu05":15}
the value of key[stu04] is : 14