This is a creation in Article, where the information may have evolved or changed. Welcome to the 13th Tutorial [Golang Series Tutorial] (/SUBJECT/2). # # What is a map? Map is the built-in type associated with the value in Go and the key (key). The value can be obtained by the corresponding key. # # How do I create a map? You can create a map by passing in the type of key and value to the ' Make ' function. ' Make (Map[type of Key]type of Value) ' is the syntax for creating a map. The code above "Gopersonsalary: = Make (Map[string]int)" creates a map named ' Personsalary ' where the key is of type string and the value is int. The 0 value of map is ' nil '. If you want to add elements to the nil map, the run-time panic will be triggered. Therefore, the map must be initialized with the ' Make ' function. "' Gopackage mainimport (" FMT ") func main () {var personsalary map[string]intif personsalary = nil {fmt. PRINTLN ("Map is nil. Going to make one. ") Personsalary = Make (Map[string]int)}} "[Online Run Program] (Https://play.golang.org/p/IwJnXMGc1M) above the program, Personsalary is nil, So you need to initialize with the Make method, and the program will output ' map is nil '. Going to make one. # # Add elements to map the syntax and arrays for adding new elements to the map are the same. The following program adds several new elements to the ' personsalary ' map. "' Gopackage mainimport (" FMT ") func main () {personsalary: = Make (Map[string]int) personsalary[" Steve "] = 12000personsalary["Jamie" = 15000personsalary["Mike"] = 9000fmt. PRINTLN ("Personsalary Map contents:", Personsalary)}"[Running Program Online] (HTTPS://PLAY.GOLANG.ORG/P/V1LNQ4IGW1) above the program output: ' Personsalary map contents:map[steve:12000 jamie:15000 MIKE:9000] ' You can also initialize the map at the time of declaration. "' Gopackage mainimport (" FMT ") func main () {personsalary: = map[string]int {" Steve ": 12000," Jamie ": 15000,}personsalary ["Mike"] = 9000fmt. PRINTLN ("Personsalary Map contents:", Personsalary)} "[Online Run Program] (https://play.golang.org/p/nlH_ADhO9f) the above program declares Personsalary, and adds two elements at the same time as the declaration. And then added the key ' Mike '. Program output: ' personsalary map contents:map[steve:12000 jamie:15000 mike:9000] ' key is not necessarily a string type. All comparable types, such as boolean,interger,float,complex,string, can be used as keys. For comparable types, visit [http://golang.org/ref/spec#Comparison_operators] (http://golang.org/ref/spec#Comparison_operators) If you want to learn more. # # to get the elements in a map now we've added several elements to map, so we're going to learn how to get them. The syntax for getting the map element is ' Map[key '. "' Gopackage mainimport (" FMT ") func main () {personsalary: = map[string]int{" Steve ": 12000," Jamie ": 15000,}personsalary ["Mike"] = 9000employee: = "Jamie" FMT. Println ("Salary of", Employee, "is", Personsalary[employee])} "[Online Running program] (HTTPS://PLAY.GOLANG.ORG/P/-TSBAC7F1V) The above program is very simple. Get and print employee ' Jamie ' salary. Program output ' Salary of Jamie is 15000 '. What happens if we get an element that doesn't exist? Map returns a value of 0 for that element type. In the ' personsalary ' map, if we get a nonexistent element, we return an ' int ' type of 0 value ' 0 '. "' Gopackage mainimport (" FMT ") func main () {personsalary: = map[string]int{" Steve ": 12000," Jamie ": 15000,}personsalary ["Mike"] = 9000employee: = "Jamie" FMT. Println ("Salary of", Employee, "is", Personsalary[employee]) fmt. Println ("Salary of Joe is", personsalary["Joe"])} "[Running Program Online] (https://play.golang.org/p/EhUJhIkYJU) above program output:" ' Salary Of Jamie is 15000Salary of the Joe is 0 "' above the program returns ' Joe ' salary is 0. We will not get any run-time errors when ' Joe ' is not included in ' Personsalary '. If we want to know if there is a "key" in the map, what to do: "' govalue, OK: = Map[key]" is the syntax for getting a key in the map. If ' OK ' is true, indicating that the key exists, the value corresponding to key is ' value ', and vice versa means that key does not exist. "' Gopackage mainimport (" FMT ") func main () {personsalary: = map[string]int{" Steve ": 12000," Jamie ": 15000,}personsalary ["Mike"] = 9000newEmp: = "Joe" value, OK: = personsalary[newemp]if OK = = true {fmt. Println ("SAlary of ", Newemp," is ", value)} else {fmt. Println (Newemp, "Not Found")}} "[Online Run Program] (https://play.golang.org/p/q8fL6MeVZs) above the program, line 15th, ' Joe ' does not exist, so ' OK ' is false. The program will output: ' Joe not found ' iterates through all the elements in the map and needs a ' for range ' loop. "' Gopackage mainimport (" FMT ") func main () {personsalary: = map[string]int{" Steve ": 12000," Jamie ": 15000,}personsalary ["Mike"] = 9000fmt. Println ("All items of a map") for key, value: = Range Personsalary {fmt. Printf ("personsalary[%s] =%d\n", key, Value)}} "[Running Program Online] (https://play.golang.org/p/gq9ZOKsI9b) above program output: ' ' All items ' of a mappersonsalary[mike] = 9000personsalary[steve] = 12000personsalary[jamie] = 15000 "__ is a bit important when using ' for range ' to traverse the map , it is not guaranteed that the order of elements obtained by the executing program is the same. __## Delete the elements in the map remove the syntax for ' key ' in ' map ' [_delete (Map, key) _] (https://golang.org/pkg/builtin/#delete). This function has no return value. "' Gopackage mainimport (" FMT ") func main () {personsalary: = map[string]int{" Steve ": 12000," Jamie ": 15000,}personsalary ["Mike"] = 9000fmt. PRINTLN ("Map before deletion", personsalary) Delete (Personsalary, "Steve ") Fmt. PRINTLN ("Map after deletion", personsalary)} "[Online Run Program] (HTTPS://PLAY.GOLANG.ORG/P/NROJZEF-A7) The above program removed the key" Steve ", Output: ' "Map before deletion map[steve:12000 jamie:15000 mike:9000]map after deletion map[mike:9000 jamie:15000]" ' # # Get the length of the map obtained Take the length of the map using the [Len] (https://golang.org/pkg/builtin/#len) function. "' Gopackage mainimport (" FMT ") func main () {personsalary: = map[string]int{" Steve ": 12000," Jamie ": 15000,}personsalary ["Mike"] = 9000fmt. Println ("Length is", Len (personsalary))} "[Online Run Program] (Https://play.golang.org/p/8O1WnKUuDP) _len in the above program (personsalary ) _ function Gets the length of the map. Program output ' length is 3 '. # # Map is a reference type similar to [slices] (https://golangbot.com/arrays-and-slices/), and map is also a reference type. When a map is assigned a new variable, they point to the same internal data structure. Therefore, changing one of the variables will affect the other variable. "' Gopackage mainimport (" FMT ") func main () {personsalary: = map[string]int{" Steve ": 12000," Jamie ": 15000,}personsalary ["Mike"] = 9000fmt. Println ("Original person salary", personsalary) Newpersonsalary: = personsalarynewpersonsalary["Mike"] = 18000fmt. Println ("Person salary CHAnged ", Personsalary)} ' [Online Run Program] (HTTPS://PLAY.GOLANG.ORG/P/OGFL3ADDQ1) above the 14th line of the program, ' Personsalary ' is assigned to ' Newpersonsalary '. On the next line, ' Mike ' in ' Newpersonsalary ' has become ' 18000 '. The ' Mike ' salary in ' personsalary ' will also become ' 18000 '. Program output: ' ' Original person salary map[steve:12000 jamie:15000 Mike:9000]person salary changed map[steve:12000 jamie:15000 MIKE:18000] "The same happens when map is passed as a function parameter. Any modifications to the map in the function are visible to external calls. # # Map Equality map cannot be judged by the ' = = ' operator, ' = = ' can only be used to check if the map is ' nil '. "' Gopackage MainFunc Main () {map1: = map[string]int{" One ": 1," one ": 2,}map2: = map1if Map1 = map2 {}}" [Run Program Online] (https:/ /PLAY.GOLANG.ORG/P/MALQDYWKCT) above program throws compilation error **invalid Operation:map1 = = MAP2 (map can only is compared to nil) * *. The way to determine whether two maps are equal is to traverse each element in the comparison of two maps. I suggest you write a program like this to implement this function:). I have implemented all the concepts we have discussed in a program. You can download the code from [GitHub] (https://github.com/golangbot/maps). This is map. Thank you for reading. Good * * Previous tutorial-[Variadic Function] (https://studygolang.com/articles/12173) * * * Next tutorial-[string] (https://studygolang.com/articles/12261) * *
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Author: Nick Coghlan Translator: arisaries proofreading: Noluye
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