The 5th Lesson Go map

This is a creation in Article, where the information may have evolved or changed.

 PackageMainImport("FMT")/ * Map-similar to a hash table or dictionary in other languages, store data in key-value form-key must be support = = or! = The type of the comparison operation, cannot be a function, map or Slice-map lookup is faster than a linear search ihenduo, but 100 times times slower than the type of data accessed using the index-MAP use make () to create, support: = This shorthand method-make ([Keytype]valuet YPE,CAP), the CAP represents capacity, can be omitted-the capacity is automatically expanded when exceeded, but as far as possible to provide a reasonable initial value-use Len () to get the number of elements-key value pairs do not exist automatically added, use delete () delete a key value pair-use for range to map and s Lice iterative Operation * /funcMain () {varMMap[int]stringm =Map[int]string{} fmt. Println (M)//completed the initialization of a map    varNMap[int]stringn = Make(Map[int]string) FMT. PRINTLN (N)//You can also use make to createP: = Make(Map[int]string) FMT. PRINTLN (P)//Yes, it is.Fmt. Println ("-----") m[1] ="OK"A: = M[2] FMT. Println (a)//Output emptyFmt. Println (M[1])Delete(M,1)//DeleteFmt. Println (M[1])//Delete output empty after    //operation of simple mapFmt. Println ("-----")}

 PackageMainImport("FMT")funcMain () {varMMap[int]Map[int]string     //Create a two layer map herem = Make(Map[int]Map[int]string)//Only one layer of map is initialized hereA, OK: = M[2][1]///Only one return value is returned when the value is taken, the second return value returns whether the key value pair exists    if!ok {//If OK does not exist, initialize the second layer of mapM[2] = Make(Map[int]string)} m[2][1] ="Good"A, OK = m[2][1] FMT. Println (A, OK)//Complex map Operations}

Slice under the For-range

package mainimport (    "fmt")func main() {    forrange slice {        //返回slice相对应的索引，i相当于计数器，v相当于slice所存储的值，是拷贝，不会影响slice本身        //可以通过slice[i]对slice本身进行操作    }}

For-range under the map

package mainimport (    "fmt")func main() {    forrangemap {        //返回k,v键值对（同样是拷贝）        //当然可以对m[k]直接对map进行操作    }}

For-range for map initialization

 PackageMainImport("FMT")funcMain () {sm: = Make([]Map[int]string,5)//This is a map-element slice that initializes the capacity, element 5     for_, V: =RangeSM {v = Make(Map[int]string,1) v[1] ="OK"Fmt. Println (v)} FMT. PRINTLN (SM)/ * Output result Map[1:ok] Map[1:ok] map[1:ok] Map[1:ok] Map[1:ok] [map[] map[ ] map[] map[] map[] "It is clear that V is a copy and cannot operate on the map itself. If you want to operate on itself, you need to make the following modifications (using i) */SMM: = Make([]Map[int]string,5) forI: =RangeSM {Smm[i] = Make(Map[int]string,1) Smm[i][1] ="OK"Fmt. Println (Smm[i])} FMT. PRINTLN (SMM)}

Indirect ordering of maps

 PackageMainImport("FMT"    "Sort")funcMain () {//Indirect ordering of mapsM: =Map[int]string{1:"a",2:"B",3:"C",4:"D",5:"E"} s: = Make([]int,Len(m)) I: =0     forK, _: =Rangem {S[i] = k i++}//Map has been deposited into sliceFmt. PRINTLN (s)//Each time the print is found to be different, it manifests the disorder of mapSort. Ints (s)//Sort the sliceFmt. PRINTLN (s)//Every time the printed out is ordered    //We can only implement the indirect ordering of maps, because map is unordered, we can only extract post-orderFmt. Println (M)}