2.39. Go language Map (Collection)

Map is a collection of unordered key-value pairs. The most important point of Map is passing the key to retrieve data quickly key , similar to an index, points to the value of the data.

Map is a collection, so we can iterate over it like arrays and slices. But, Map is unordered, and we cannot determine the order in which it isreturned, because Map is to use the hash table to achieve.

2.39.1. Define Map #

You can use built-in functions make , you can also use the map keyword to define Map :

/* Declare variables, default map is nil */
var map_variable map[key_data_type]value_data_type

/* Using the make function */
map_variable := make(map[key_data_type]value_data_type)

If you don’t initialize map then a nil map . nil map cannot be used to store key-value pairs

2.39.2. Example #

The following example demonstrates the creation and use of map :

Example #

package main
import "fmt"
func main() {
    var countryCapitalMap map[string]string /*Create Collection */
    countryCapitalMap = make(map[string]string)
    /* Insert key value pairs into the map, corresponding to
    the capital cities of each country */
    countryCapitalMap [ "France" ] = "Paris"
    countryCapitalMap [ "Italy" ] = "Rome"
    countryCapitalMap [ "Japan" ] = "Tokyo"
    countryCapitalMap [ "India " ] = "New Delhi"
    /*Use the key to output map values */
    for country := range countryCapitalMap {
        fmt.Println(country, "The capital is", countryCapitalMap [country])
    }
    /*Check if the element exists in the collection */
    capital, ok := countryCapitalMap [ "American" ]
/*If it is determined to be true, then it exists;
    otherwise, it does not exist */
    /*fmt.Println(capital) */
    /*fmt.Println(ok) */
    if (ok) {
        fmt.Println("The capital of America is", capital)
    } else {
        fmt.Println("The capital city of America does not exist")
    }
}

The running result of the above instance is as follows:

The capital of France is Paris
Italy's capital is Rome
The capital of Japan is Tokyo
India's capital is New Delhi
The capital city of America does not exist

2.39.3. `delete()` function #

delete() function is used to delete the elements of the collection, and the argument is map and its corresponding key . Examples are as follows:

Example #

package main
import "fmt"
func main() {
        /* Create a map */
        countryCapitalMap := map[string]string{"France": "Paris",
"Italy": "Rome", "Japan": "Tokyo", "India": "New delhi"}
        fmt.Println("Original Map")
        /* Print Map */
        for country := range countryCapitalMap {
                fmt.Println(country, "The capital is", countryCapitalMap [
country ])
        }
        /*Delete Element*/ delete(countryCapitalMap, "France")
        fmt.Println("French entry deleted")
        fmt.Println("Map after deleting elements")
        /*Print Map*/
        for country := range countryCapitalMap {
                fmt.Println(country, "The capital is", countryCapitalMap [
country ])
        }
}

The running result of the above instance is as follows:

Original map
The capital of India is New delhi
The capital of France is Paris
Italy's capital is Rome
Japan's capital is Tokyo
French entry deleted
Map after deleting elements
Italy's capital is Rome
Japan's capital is Tokyo
The capital of India is New delhi