使用嵌套映射来压缩字符串时无法获得适当的输出

Question

I'm new with galang and I want to concat string with nested map. Below is the dummy code given, point out my mistake. Thanks in advance

    import (
    "fmt"
    "strconv"
    )

    func main() {
    str := "Hello @John martin #sosos &Hi @William "
    var key string = ""
    var ku int = 0
    var kh int = 0
    var kg int = 0
    var id string
    var col string 
    var retMap = make(map[string]map[string]string)
    retMap[key] = make(map[string]string)    
    for i := 0; i < len(str); i++ {
      //fmt.Println(string(str[i]), " >> ", str[i])
      if str[i] == 64 || str[i] == 35 || str[i] == 38 {
        if str[i] == 64 {
          ku++
          key = "user"
          id = strconv.Itoa(ku)
      } else if str[i] == 35 {
        kh++
        key = "hashTag"
        id = strconv.Itoa(kh)
      } else {
        kg++
        key = "group"
        id = strconv.Itoa(kg)
      }
      retMap[key] = make(map[string]string) // If not assign here then it gives runtime error "panic: assignment to entry in nil map"
      for j := i + 1; j < len(str); j++ {
        col = col + string(str[j])
        if str[j] == 32 {
          j = len(str) - 1
          retMap[key][id] = retMap[key][id] + col
          col = " "
        }
      }
    }
 }
 fmt.Println("Final String ",retMap)
}

Output : Final String map[group:map[1: Hi ] user:map[2: William ] hashTag:map[1: sosos ]]

Expected Output :

Final String map[group:map[1: Hi ] user:map[1: John, 2: William ] hashTag:map[1: sosos ]]

It might be duplicate of

Runtime error: "assignment to entry in nil map"

Runtime error: assignment to entry in nil map

but not understand kindly provide me a solution. Thanks

Answer 1

The issue is that you are initializing the nested map of "key" in each called, so it always overrides the previous data.

So just changing your line

retMap[key] = make(map[string]string) // If not assign here then it gives runtime error "panic: assignment to entry in nil map"

to the below should make your code work:

=_, ok := retMap[key]
if !ok {
    retMap[key] = make(map[string]string)
}

I'm just checking the existence of a value stored for "key", and initialize a new map if it doesn't exist.

---

Updated:

I also rewrote your code to use some built-in functions that Go provide with, as strings.Split or strings.Trim* functions. It could be helpful.

package main

import (
    "fmt"
    "strconv"
    "strings"
)

const str = "Hello @John martin #sosos &Hi @William "

func main() {
    retMap := make(map[string]map[string]string)
    retMap["group"] = make(map[string]string)
    retMap["user"] = make(map[string]string)
    retMap["hashTag"] = make(map[string]string)
    list := strings.Split(strings.TrimSpace(str), " ")

    for _, value := range list {
        firstCharacter := string(value[0])
        if firstCharacter == "@" {
            retMap["user"][strconv.Itoa(len(retMap["user"])+1)] = strings.TrimLeft(value, "@")
        } else if firstCharacter == "&" {
            retMap["group"][strconv.Itoa(len(retMap["group"])+1)] = strings.TrimLeft(value, "&")
        } else if firstCharacter == "#" {
            retMap["hashTag"][strconv.Itoa(len(retMap["hashTag"])+1)] = strings.TrimLeft(value, "#")
        }
    }

    fmt.Println("Final String ", retMap)
}