YouTipGo Map
# Go Language Map (Collection)
A Map is an unordered collection of key-value pairs.
The most important aspect of a Map is the ability to quickly retrieve data using a key, which acts like an index pointing to the value.
A Map is a collection, so we can iterate over it like we do with arrays and slices. However, Maps are unordered, meaning the order of key-value pairs returned when iterating over a Map is not guaranteed.
When retrieving a value from a Map, if the key does not exist, the zero value of the value's type is returned. For example, the zero value for an `int` is `0`, and for a `string` it is `""`.
Maps are reference types. If you pass a Map to a function or assign it to another variable, they both point to the same underlying data structure. Therefore, modifications to the Map will affect all variables that reference it.
### Defining a Map
You can define a Map using the built-in `make` function or the `map` keyword:
/* Using the make function */ map_variable := make(mapValueType, initialCapacity)
Where `KeyType` is the type of the key, `ValueType` is the type of the value, and `initialCapacity` is an optional parameter to specify the initial capacity of the Map. The capacity of a Map is the number of key-value pairs it can hold. When the number of key-value pairs reaches the capacity, the Map will automatically expand. If `initialCapacity` is not specified, Go will choose a suitable value based on the actual situation.
## Example
// Create an empty Map
m :=make(mapint)
// Create a Map with an initial capacity of 10
m :=make(mapint,10)
You can also create a Map using a literal:
// Create a Map using a literal m := mapint{ "apple": 1, "banana": 2, "orange": 3,}
Retrieve elements:
// Retrieve a key-value pair v1 := m v2, ok := m // If the key does not exist, ok is false, and v2 is the zero value of the type
Modify elements:
// Modify a key-value pair m = 5
Get the length of the Map:
// Get the length of the Map len := len(m)
Iterate over the Map:
// Iterate over the Mapfor k, v := range m { fmt.Printf("key=%s, value=%dn", k, v)}
Delete elements:
// Delete a key-value pairdelete(m, "banana")
### Example
The following example demonstrates creating and using a map:
## Example
package main
import"fmt"
func main(){
var siteMap mapstring/*Create a collection */
siteMap =make(mapstring)
/* Insert key-value pairs into the map, mapping countries to their capitals */
siteMap ="Google"
siteMap =""
siteMap ="Baidu"
siteMap ="Wikipedia"
/* Output map values using keys */
for site :=range siteMap {
fmt.Println(site,"capital is", siteMap )
}
/* Check if an element exists in the collection */
name, ok := siteMap /*If it exists, ok is true; otherwise, it's false */
/*fmt.Println(capital) */
/*fmt.Println(ok) */
if(ok){
fmt.Println("Facebook's site is", name)
}else{
fmt.Println("Facebook site does not exist")
}
}
The output of the above example is:
Wiki capital is WikipediaGoogle capital is GoogleTutorial capital is Baidu capital is BaiduFacebook site does not exist
* * *
## delete() Function
The `delete()` function is used to delete elements from a collection. Its parameters are the map and the corresponding key. Example:
## Example
package main
import"fmt"
func main(){
/* Create a map */
countryCapitalMap :=mapstring{"France":"Paris","Italy":"Rome","Japan":"Tokyo","India":"New delhi"}
fmt.Println("Original map")
/* Print the map */
for country :=range countryCapitalMap {
fmt.Println(country,"capital is", countryCapitalMap )
}
/* Delete an element */ delete(countryCapitalMap,"France")
fmt.Println("France entry deleted")
fmt.Println("Map after deletion")
/* Print the map */
for country :=range countryCapitalMap {
fmt.Println(country,"capital is", countryCapitalMap )
}
}
The output of the above example is:
Original mapIndia capital is New delhi France capital is ParisItaly capital is RomeJapan capital is TokyoFrance entry deletedMap after deletionItaly capital is RomeJapan capital is TokyoIndia capital is New delhi