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Deleting an element from a slice in Go

Deleting an element from a slice in Go

Clive B.

—

The Problem

You don’t know how to delete an element from a slice in Go.

The Solution

If you know the index of the element(s) that you want to delete from a slice, you can use the Delete function from the slices package.

Note: The slices.Delete function is O(len(s)-i), where i represents the start of the range to be deleted. If you need to delete many items, it is better to delete them all in a single call than to delete one item at a time. This function also expects the input to be valid.

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package main

import (
    "fmt"
    "slices"
)

func main() {
    letters := []string{"a", "b", "c", "d", "e"}
    letters = slices.Delete(letters, 1, 4)
    fmt.Println(letters)
}

This prints:

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[a e]

Attempting to delete an invalid range will cause a panic, as in the example below:

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package main

import (
    "fmt"
    "slices"
)

func main() {
    letters := []string{"a", "b", "c", "d", "e"}
    letters = slices.Delete(letters, 1, 10)
}

Because 10 is an invalid index, this returns the following panic:

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panic: runtime error: slice bounds out of range [:10:5]

Searching for Elements

If you want to search for specific elements in a slice, you can use the slices.DeleteFunc instead.

For example, you could search for all the even numbers in a slice as follows:

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package main

import (
    "fmt"
    "slices"
)

func main() {
    example := []int{0, 1, 2, 3, 4, 5, 6}
    example = slices.DeleteFunc(example, func(n int) bool {
        return n%2 != 0 // Remove odd numbers.
    })

    fmt.Println(example)
}

This prints an output of the slice with the odd numbers removed:

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[0 2 4 6]

Note: This example passes the func(n int) filter function to slices.DeleteFunc. Because this is a generic filter function, its argument must match the type of the slice. In this case, it accepts an int because example is a slice of integers. If you instead wanted to filter a specific string from strings, you would change the argument of the filter function to string:

Click to Copy
package main

import (
    "fmt"
    "slices"
)

func main() {
    example := []string{"a", "b", "c"}
    example = slices.DeleteFunc(example, func(s string) bool {
        return s == "b"
    })

    fmt.Println(example)
}

This would print:

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[a c]

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