Deleting from a map

Learn to delete elements from a map with the delete function.

Deleting from a map

The built-in delete(m, key) function removes the key from the map. If the key doesn't exist nothing happens; it doesn't error either:

stok := map[string]int{"kalem": 3, "silgi": 0}
delete(stok, "silgi")
delete(stok, "yok")   // no problem
fmt.Println(len(stok))  // 1

To remove all keys, clear(m) is available since Go 1.21.

Cleaning by condition

Cleaning out products that are out of stock in a single loop:

for ad, adet := range stok {
    if adet == 0 {
        delete(stok, ad)
    }
}

maps.DeleteFunc(stok, func(k string, v int) bool { return v == 0 }), added in Go 1.21, does the same in one line.

Exercise Stock cleanup

Declare stok := map[string]int{"kalem": 3, "silgi": 0, "defter": 5, "cetvel": 0}. Delete the ones with quantity 0 using range + delete and print the number of remaining keys.

Show example solution

package main

import "fmt"

func main() {
    stok := map[string]int{"kalem": 3, "silgi": 0, "defter": 5, "cetvel": 0}
    for ad, adet := range stok {
        if adet == 0 {
            delete(stok, ad)
        }
    }
    fmt.Println(len(stok))
}

Test yourself

Is it safe to delete elements while iterating over a map with <code>range</code>?
- It doesn't compile
- Yes; Go explicitly supports it
- No, it panics
- Only on the last element
Show answer

Yes; Go explicitly supports it — Keys deleted during iteration that haven't been seen yet won't come up; deleting is safe.

Delete the key

____(sepet, "kalem")

Show answer

delete(sepet, "kalem")

Operation and result

delete(m, "var")

The key is removed
delete(m, "yok")

Nothing happens
clear(m)

All keys are removed
maps.DeleteFunc

Deletes by condition

Next lesson: Iterating a map with range

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