How to split a slice into equally sized chunks in Go

Created Apr 9, 2022 at 11:40

Modified Apr 18, 2022 at 10:34

Using for Loop

The easiest method involves iterating over the slice and incrementing by the chunk size. An implementation is shown in the section below.

package main

import "fmt"

func chunkSlice(slice []int, chunkSize int) ([][]int, error) {

  chunks := make([][]int, 0, (len(slice)+chunkSize-1)/chunkSize)
  for chunkSize < len(slice) {
    slice, chunks = slice[chunkSize:], append(chunks, slice[0:chunkSize:chunkSize])
  }
  chunks = append(chunks, slice)

  return chunks, nil
}

func main() {

  slice := []int{1, 2, 3, 4, 5, 6, 7}

  chunks, _ := chunkSlice(slice, 3)
  fmt.Println(chunks)
}

[[1 2 3] [4 5 6] [7]]

You can use reflect.TypeOf for any []T.

Another variant

A general solution to split a slice to into sub-slices of equal length.

package main

import "fmt"

func chunkSlice(slice []int, chunkSize int) ([][]int, error) {

  chunks := make([][]int, 0, (len(slice)+chunkSize-1)/chunkSize)

  var j int
  for i := 0; i < len(slice); i += chunkSize {
    j += chunkSize
    if j > len(slice) {
      j = len(slice)
    }
    chunks = append(chunks, slice[i:j])
  }

  return chunks, nil
}

func main() {

  slice := []int{1, 2, 3, 4, 5, 6, 7}

  chunks, _ := chunkSlice(slice, 3)
  fmt.Println(chunks)
}