I am learning to use the map of maps. In the following example, there are three nested maps.
package main import ( "fmt" ) func main() { var data = map[string]map[string]map[string]string{} data["Date_1"] = map[string]map[string]string{} data["Date_1"] = make(map[string]map[string]string, 1) data["Date_1"] = make(map[string]map[string]string, 0) data["Date_1"]["Sistem_A"] = map[string]string{} data["Date_1"]["Sistem_A"] = make(map[string]string, 0) data["Date_1"]["Sistem_A"] = make(map[string]string, 0) data["Date_1"]["Sistem_A"]["command_1"] = "white" data["Date_1"]["Sistem_A"]["command_2"] = "blue" data["Date_1"]["Sistem_A"]["command_3"] = "red" fmt.Println("data: ", data) } Output
data: map[Date_1:map[Sistem_A:map[command_1:white command_2:blue command_3:red]]] The problem is that if I want to add the values in one step I get a panic: assignment to entry in nil map.
package main import ( "fmt" ) func main() { var data = map[string]map[string]map[string]string{} data["Date_1"] = map[string]map[string]string{} data["Date_1"] = make(map[string]map[string]string, 0) data["Date_1"] = make(map[string]map[string]string, 0) data["Date_1"]["Sistem_A"] = map[string]string{} data["Date_1"]["Sistem_A"] = make(map[string]string, 0) data["Date_1"]["Sistem_A"] = make(map[string]string, 0) data["Date_1"]["Sistem_A"]["command_1"] = "white" data["Date_1"]["Sistem_A"]["command_2"] = "blue" data["Date_1"]["Sistem_A"]["command_3"] = "red" data["Date_2"]["Sistem_A"]["command_5"] = "violet" fmt.Println("data: ", data) } Output
panic: assignment to entry in nil map There is very little guidance information at this point. Could you help me?
Thank you.
2 Answers
It is here:
data["Date_2"]["Sistem_A"]["command_5"] = "violet" The expression data["Date_2"] will return a nil-map. It is never initialized, so looking for the index ["Sistem_A"] panics. Initialize the map first:
data["Date_2"] = make(map[string]map[string]string) data["Date_2"]["Sistem_A"] = make(map[string]string) data["Date_2"]["Sistem_A"]["command_5"] = "violet" Your problem is, that you never initialized data["Date_2"] (so it is nil).
So by doing data["Date_2"]["Sistem_A"]["command_5"] = "violet", looking for the index panics.
you have to initialize first as follows:
data["Date_2"]=make(map[string]map[string]string) data["Date_2"]["Sistem_A"]=make(map[string]string) 
