{"id":267,"date":"2024-09-15T11:09:58","date_gmt":"2024-09-15T04:09:58","guid":{"rendered":"https:\/\/gotutorial.org\/?page_id=267"},"modified":"2024-09-26T11:20:08","modified_gmt":"2024-09-26T04:20:08","slug":"go-map","status":"publish","type":"page","link":"https:\/\/www.gotutorial.org\/go-tutorial\/go-map\/","title":{"rendered":"Go Map"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you will learn about the Go Map type and how to use it to associate keys with values.<\/p>\n\n\n\n

In Go, a map is a built-in type that associates keys with values. A map is similar to a hash table or dictionary in other programming languages.<\/p>\n\n\n\n

Unlike arrays<\/a> or slices<\/a>, elements in a map do not have any particular order.<\/p>\n\n\n\n

Declaring a map<\/h2>\n\n\n\n

To declare a map, you use a map<\/code> keyword, followed by the type of keys, and the type of values:<\/p>\n\n\n

var<\/span> mapName map[keyType] valueType<\/code><\/span>Code language:<\/span> JavaScript<\/span> (<\/span>javascript<\/span>)<\/span><\/small><\/pre>\n\n\n
For example:<\/p>\n\n\n
var<\/span> languages map[string] string<\/code><\/span>Code language:<\/span> JavaScript<\/span> (<\/span>javascript<\/span>)<\/span><\/small><\/pre>\n\n\n
In this example, we declare a map called languages<\/code> with types of keys and values are string<\/code>.<\/p>\n\n\n\n
Alternatively, you can use the make()<\/code> function to create a map:<\/p>\n\n\n
var<\/span> languages = make(map[string] string)<\/code><\/span>Code language:<\/span> JavaScript<\/span> (<\/span>javascript<\/span>)<\/span><\/small><\/pre>\n\n\n
Initializing a map<\/h2>\n\n\n\n
To initialize a map, you can use a map literal as follows:<\/p>\n\n\n
var<\/span> languages = map[string]string {\n    \"go\"<\/span>: \"Go\"<\/span>,\n    \"js\"<\/span>: \"javascript\"<\/span>,\n    \"py\"<\/span>: \"python\"<\/span>,\n}<\/code><\/span>Code language:<\/span> JavaScript<\/span> (<\/span>javascript<\/span>)<\/span><\/small><\/pre>\n\n\n
In this example, we specify a list of key\/value pairs for the languages<\/code> map, where keys are the file extensions and values are programming languages.<\/p>\n\n\n\n
Note that the keys of a map must be unique. If you add a new element with an existing key, Go will overwrite the previous value.<\/p>\n\n\n\n
languages := map[string]string{\n    \"go\"<\/span>: \"Go\"<\/span>,\n    \"js\"<\/span>: \"javascript\"<\/span>,\n    \"py\"<\/span>: \"python\"<\/span>,\n}<\/code><\/span>Code language:<\/span> JavaScript<\/span> (<\/span>javascript<\/span>)<\/span><\/small><\/pre>\n\n\n
Adding elements<\/h2>\n\n\n\n
To add an element to a map, you specify a key and a value:<\/p>\n\n\n
mapName[key] = value<\/code><\/span><\/pre>\n\n\n
For example:<\/p>\n\n\n
languages[\"php\"<\/span>] = \"PHP\"<\/span><\/code><\/span>Code language:<\/span> JavaScript<\/span> (<\/span>javascript<\/span>)<\/span><\/small><\/pre>\n\n\n
If you use an existing key, Go will overwrite the previous value with the new value.<\/p>\n\n\n\n
Retrieving elements<\/h2>\n\n\n\n
To retrieve a value by key, you specify the key inside the square brackets:<\/p>\n\n\n
lang := languages[\"go\"<\/span>]<\/code><\/span>Code language:<\/span> JavaScript<\/span> (<\/span>javascript<\/span>)<\/span><\/small><\/pre>\n\n\n
Checking for existence<\/h2>\n\n\n\n
When getting a value, you can check if the key exists using the second return value, for example:<\/p>\n\n\n
lang, exists<\/span> := languages[\"css\"<\/span>]\nif<\/span> exists {\n    fmt.Println(lang)\n} else<\/span> {\n    fmt.Println(\"Not found\"<\/span>)\n}<\/code><\/span>Code language:<\/span> JavaScript<\/span> (<\/span>javascript<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
Not found<\/code><\/span>Code language:<\/span> JavaScript<\/span> (<\/span>javascript<\/span>)<\/span><\/small><\/pre>\n\n\n
In this example, if the css<\/code> key exists in the languages<\/code> map, the exists<\/code> variable will be set to true or false otherwise. <\/p>\n\n\n\n
Since the languages<\/code> map does not have the css<\/code> key, the output shows \"Not found\"<\/code>.<\/p>\n\n\n\n
Deleting elements<\/h2>\n\n\n\n
To delete an element by a key, you use the built-in delete()<\/code> function. For example, the following deletes the element with the key py<\/code> in the languages<\/code> map:<\/p>\n\n\n
delete<\/span>(languages,\"py\"<\/span>)<\/code><\/span>Code language:<\/span> JavaScript<\/span> (<\/span>javascript<\/span>)<\/span><\/small><\/pre>\n\n\n
Iterating over elements of a map<\/h2>\n\n\n\n
To iterate over elements of a map, you use a for range<\/a> loop. The first variable is the key and the second variable is the value. For example:<\/p>\n\n\n
for<\/span> key, value<\/span> := range languages {\n    fmt.Println(key, value)\n}<\/code><\/span>Code language:<\/span> JavaScript<\/span> (<\/span>javascript<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
go Go\njs javascript\nphp PHP<\/code><\/span>Code language:<\/span> JavaScript<\/span> (<\/span>javascript<\/span>)<\/span><\/small><\/pre>\n\n\n
If you use one loop variable, it will be the key:<\/p>\n\n\n
package main\n\nfunc main() {\n    languages<\/span> := map[string]string{\n        \"go\"<\/span>: \"Go\"<\/span>,\n        \"js\"<\/span>: \"javascript\"<\/span>,\n        \"py\"<\/span>: \"python\"<\/span>,\n    }\n\n    for<\/span> key := range languages {\n        println(key)\n    }\n}<\/code><\/span>Code language:<\/span> JavaScript<\/span> (<\/span>javascript<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
go\njs\npy<\/code><\/span><\/pre>\n\n\n
Putting it all together<\/h2>\n\n\n
package main\n\nimport<\/span> \"fmt\"<\/span>\n\nfunc main() {\n    \/\/ var languages = map[string]string{<\/span>\n    \/\/     \"go\": \"Go\",<\/span>\n    \/\/     \"js\": \"javascript\",<\/span>\n    \/\/     \"py\": \"python\",<\/span>\n    \/\/ }<\/span>\n\n    languages<\/span> := map[string]string{\n        \"go\"<\/span>: \"Go\"<\/span>,\n        \"js\"<\/span>: \"javascript\"<\/span>,\n        \"py\"<\/span>: \"python\"<\/span>,\n    }\n\n    \/\/ add an element<\/span>\n    languages[\"php\"<\/span>] = \"PHP\"<\/span>\n\n    \/\/ checking existence<\/span>\n    lang, exists<\/span> := languages[\"css\"<\/span>]\n    if<\/span> exists {\n        fmt.Println(lang)\n    } else<\/span> {\n        fmt.Println(\"Not found\"<\/span>)\n    }\n    \/\/ delete an element<\/span>\n    delete<\/span>(languages, \"py\"<\/span>)\n\n    \/\/ iterate over map with range<\/span>\n    for<\/span> key, value<\/span> := range languages {\n        fmt.Println(key, value)\n    }\n}<\/code><\/span>Code language:<\/span> JavaScript<\/span> (<\/span>javascript<\/span>)<\/span><\/small><\/pre>\n\n\n
Summary<\/h2>\n\n\n\n
    \n
  • A map is a data structure that associates keys with values.<\/li>\n\n\n\n
  • Use the make()<\/code> function to create a map.<\/li>\n\n\n\n
  • Use the for range<\/code> loop to iterate over map elements.<\/li>\n<\/ul>\n
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Inside a function<\/a>, you can declare and initialize a map using a short variable declaration as follows:<\/p>\n\n\n