08-Maps

Maps

map is built in the value type associated Go (value) of the key (key) is. Values can be acquired by a corresponding key. Maps similar to the dictionary in python

Maps definitions

maps the key value must be a hash (are immutable types: string, numeric ...) (the Map are unordered)

maps creation statement: var A Map [key type] value Value Type
 
Package main 
Import  " FMT " 

FUNC main () { 
    var A Map [int] String #key is int, value is String 
    fmt.Println (A) 
} 
# Results 
Map []    null #map type is nil

maps assignment and initialization values

Package main
 Import  " FMT " 

FUNC main () { 
    var b map [int] int = the make (map [int] int) # use map initialization 
    b [. 1] = 100     # to b which set value, key value form 
    b [2 ] = 50 
    fmt.Println (B) 
    fmt.Println (B [ 1])   # 1 acquires a value of the key value to 
}
 # results 
Map [1: 100 2:50 ]
 100

Take a non-existent key value what will happen? (Returns the value null values)

main Package
 Import  " FMT " 

FUNC main () { 
    var Map B [int] int = the make (Map [int] int) 
    B [ . 1] = 100 
    B [ 2] = 50 
    fmt.Println (B [ . 5 ])   # go value 5 key value, whichever is less. Because the value is of type int and the printed 0 
} 
# Results 
0

We want to know in the end the map is not the existence of this key, you can judge by ok. If ok is true that the presence of the key, the corresponding value is the key value, and vice versa indicates key does not exist.

package main
import "fmt"

func main() {
    var b map[int]int=make(map[int]int)
    b[1]=100
    b[2]=50
    fmt.Println(b)
    fmt.Println(b[1]) #100
    fmt.Println(b[5])  #0
    v,ok:=b[1]
    if ok==true {    #判断
        fmt.Println(v)  #100
    }
}

A second way to define and initialize

main Package
 Import  " FMT " 

FUNC main () { 
    var A = Map [int] {String. 1: "10", 2: "20 is" } # Key, in the form of value initialization value 
    fmt.Println (A [ . 1 ]) # 10 
} 
# results 
10

Delete the map elements

Delete map the key syntax is [ the Delete (the Map, Key) ]. This function does not return a value.

main Package
 Import  " FMT " 

FUNC main () {     
    var A = Map [int] {String. 1: " 10 " , 2: " 100 " }
     Delete (A, 2 ) can only be deleted exists # Key 
    Delete (A, . 3 )   # without this key will not delete 
    fmt.Println (A) 
} 
# results 
map [1:10]

Get the length of the map

package main
import "fmt"

func main() {
    var a =map[int]string{1:"10",2:"100"}
    fmt.Println(len(a))
}
#结果
2

Map is a reference type

map is a reference type. When the map is assigned to a new variable, they point to the same internal data structure. Therefore, changing one variable will affect other variables .

main Package
 Import  " FMT " 
FUNC main () { 

    var A = Map [int] {String. 1: " 10 " , 2: " 100 " } 
    test2 (A) 
    fmt.Println (A) 
} 
FUNC test2 (A Map [int ] String) { 
    a [ . 1] = " 20 is "   # test1 is a modification will affect the original a 
    fmt.Println (a) 
} 
# results 
Map [1:20 2: 100 ] 
Map [ 1:20 2: 100 ]

Map for equality

can not be used between the map == operator judgment, == it can only be used to check whether the map nil.

The method of determining whether two map is equal to compare two traverse map each element

Map cycle all the elements

Method 1: The for loop, this approach is not advocated

var a =map[int]string{1:"10",0:"100",10:"999"}
for i:=0;i<len(a);i++{
    fmt.Println(a[i])
}

Method 2: The way for range and

var a =map[int]string{1:"10",0:"100",10:"999"}

for k, i = range {a 
    fmt.Println (a) 
    fmt.Println (v) 
}

Added: Slice remove elements

The index taken, then placed in a new array

var a =[]int{1,2,3,4,5,6}
a=append(a[0:2],a[3:]...)
fmt.Println(a)

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