CODEWITHSUNDEEP
loopsdictionarygo
Martin Redmond
Martin Redmond

Reputation: 13996

Iterating over all the keys of a map

Is there a way to get a list of all the keys in a Go language map? The number of elements is given by len(), but if I have a map like:

m := map[string]string{ "key1":"val1", "key2":"val2" };

How do I iterate over all the keys?

Upvotes: 464

Views: 464012

Answers (6)

ralonr
ralonr

Reputation: 438

For sorted keys of map[string]string.

package main

import (
    "fmt"
    "sort"
)

func main() {
    m := map[string]string{"key1": "val1", "key2": "val2"}
    sortStringMap(m)
}

// sortStringMap prints the [string]string as keys sorted
func sortStringMap(m map[string]string) {
    var keys []string
    for key := range m {
        keys = append(keys, key)
    }
    sort.Strings(keys)  // sort the keys
    for _, key := range keys {
        fmt.Printf("%s\t:%s\n", key, m[key])
    }
}

output:

key1    :val1
key2    :val2

Upvotes: 0

Sridhar
Sridhar

Reputation: 2532

Is there a way to get a list of all the keys in a Go language map?

ks := reflect.ValueOf(m).MapKeys()

how do I iterate over all the keys?

Use the accepted answer:

for _, k := range m { ... }

Upvotes: 20

fliX
fliX

Reputation: 813

Using Generics:

func Keys[K comparable, V any](m map[K]V) []K {
    keys := make([]K, 0, len(m))

    for k := range m {
        keys = append(keys, k)
    }

    return keys
}

Upvotes: 4

Mohsen
Mohsen

Reputation: 4266

A Type agnostic solution:

for _, key := range reflect.ValueOf(yourMap).MapKeys() {
    value := yourMap.MapIndex(key).Interface()
    fmt.Println("Key:", key, "Value:", value)
}

Upvotes: 6

Jonathan Feinberg
Jonathan Feinberg

Reputation: 45364

https://play.golang.org/p/JGZ7mN0-U-

for k, v := range m { 
    fmt.Printf("key[%s] value[%s]\n", k, v)
}

or

for k := range m {
    fmt.Printf("key[%s] value[%s]\n", k, m[k])
}

Go language specs for for statements specifies that the first value is the key, the second variable is the value, but doesn't have to be present.

Upvotes: 771

a8m
a8m

Reputation: 9474

Here's some easy way to get slice of the map-keys. 

// Return keys of the given map
func Keys(m map[string]interface{}) (keys []string) {
    for k := range m {
        keys = append(keys, k)
    }
    return keys
}

// use `Keys` func
func main() {
    m := map[string]interface{}{
        "foo": 1,
        "bar": true,
        "baz": "baz",
    }
    fmt.Println(Keys(m)) // [foo bar baz]
}

Upvotes: 21

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