Split string by length in Golang

Question

Does anyone know how to split a string in Golang by length?

For example to split "helloworld" after every 3 characters, so it should ideally return an array of "hel" "low" "orl" "d"?

Alternatively a possible solution would be to also append a newline after every 3 characters..

All ideas are greatly appreciated!

Answer 1

An easy solution using regex

re := regexp.MustCompile((\S{3})) x := re.FindAllStringSubmatch("HelloWorld", -1) fmt.Println(x)

https://play.golang.org/p/mfmaQlSRkHe

Answer 2

Make sure to convert your string into a slice of rune: see "Slice string into letters".

for automatically converts string to rune so there is no additional code needed in this case to convert the string to rune first.

for i, r := range s {
    fmt.Printf("i%d r %c\n", i, r)
    // every 3 i, do something
}

r[n:n+3] will work best with a being a slice of rune.

The index will increase by one every rune, while it might increase by more than one for every byte in a slice of string: "世界": i would be 0 and 3: a character (rune) can be formed of multiple bytes.

---

For instance, consider s := "世a界世bcd界efg世": 12 runes. (see play.golang.org)

If you try to parse it byte by byte, you will miss (in a naive split every 3 chars implementation) some of the "index modulo 3" (equals to 2, 5, 8 and 11), because the index will increase past those values:

for i, r := range s {
    res = res + string(r)
    fmt.Printf("i %d r %c\n", i, r)
    if i > 0 && (i+1)%3 == 0 {
        fmt.Printf("=>(%d) '%v'\n", i, res)
        res = ""
    }
}

The output:

i  0 r 世
i  3 r a   <== miss i==2
i  4 r 界
i  7 r 世  <== miss i==5
i 10 r b  <== miss i==8
i 11 r c  ===============> would print '世a界世bc', not exactly '3 chars'!
i 12 r d
i 13 r 界
i 16 r e  <== miss i==14
i 17 r f  ===============> would print 'd界ef'
i 18 r g
i 19 r 世 <== miss the rest of the string

But if you were to iterate on runes (a := []rune(s)), you would get what you expect, as the index would increase one rune at a time, making it easy to aggregate exactly 3 characters:

for i, r := range a {
    res = res + string(r)
    fmt.Printf("i%d r %c\n", i, r)
    if i > 0 && (i+1)%3 == 0 {
        fmt.Printf("=>(%d) '%v'\n", i, res)
        res = ""
    }
}

Output:

i 0 r 世
i 1 r a
i 2 r 界 ===============> would print '世a界'
i 3 r 世
i 4 r b
i 5 r c ===============> would print '世bc'
i 6 r d
i 7 r 界
i 8 r e ===============> would print 'd界e'
i 9 r f
i10 r g
i11 r 世 ===============> would print 'fg世'

Answer 3

Here is another example (you can try it here):

package main

import (
    "fmt"
    "strings"
)

func ChunkString(s string, chunkSize int) []string {
    var chunks []string
    runes := []rune(s)

    if len(runes) == 0 {
        return []string{s}
    }

    for i := 0; i < len(runes); i += chunkSize {
        nn := i + chunkSize
        if nn > len(runes) {
            nn = len(runes)
        }
        chunks = append(chunks, string(runes[i:nn]))
    }
    return chunks
}

func main() {
    fmt.Println(ChunkString("helloworld", 3))
    fmt.Println(strings.Join(ChunkString("helloworld", 3), "\n"))
}

Answer 4

I tried 3 version to implement the function, the function named "splitByWidthMake" is fastest.

These functions ignore the unicode but only the ascii code.

package main

import (
    "fmt"
    "strings"
    "time"
    "math"
)

func splitByWidthMake(str string, size int) []string {
    strLength := len(str)
    splitedLength := int(math.Ceil(float64(strLength) / float64(size)))
    splited := make([]string, splitedLength)
    var start, stop int
    for i := 0; i < splitedLength; i += 1 {
        start = i * size
        stop = start + size
        if stop > strLength {
            stop = strLength
        }
        splited[i] = str[start : stop]
    }
    return splited
}



func splitByWidth(str string, size int) []string {
    strLength := len(str)
    var splited []string
    var stop int
    for i := 0; i < strLength; i += size {
        stop = i + size
        if stop > strLength {
            stop = strLength
        }
        splited = append(splited, str[i:stop])
    }
    return splited
}

func splitRecursive(str string, size int) []string {
    if len(str) <= size {
        return []string{str}
    }
    return append([]string{string(str[0:size])}, splitRecursive(str[size:], size)...)
}

func main() {
    /*
    testStrings := []string{
        "hello world",
        "",
        "1",
    }
    */

    testStrings := make([]string, 10)
    for i := range testStrings {
        testStrings[i] = strings.Repeat("#", int(math.Pow(2, float64(i))))
    }

    //fmt.Println(testStrings)

    t1 := time.Now()
    for i := range testStrings {
        _ = splitByWidthMake(testStrings[i], 2)
        //fmt.Println(t)
    }
    elapsed := time.Since(t1)
    fmt.Println("for loop version elapsed: ", elapsed)


    t1 = time.Now()
    for i := range testStrings {
        _ = splitByWidth(testStrings[i], 2)
    }
    elapsed = time.Since(t1)
    fmt.Println("for loop without make version elapsed: ", elapsed)




    t1 = time.Now()
    for i := range testStrings {
        _ = splitRecursive(testStrings[i], 2)
    }
    elapsed = time.Since(t1)
    fmt.Println("recursive version elapsed: ", elapsed)

}

Answer 5

Also needed a function to do this recently, see example usage here

func SplitSubN(s string, n int) []string {
    sub := ""
    subs := []string{}

    runes := bytes.Runes([]byte(s))
    l := len(runes)
    for i, r := range runes {
        sub = sub + string(r)
        if (i + 1) % n == 0 {
            subs = append(subs, sub)
            sub = ""
        } else if (i + 1) == l {
            subs = append(subs, sub)
        }
    }

    return subs
}

Answer 6

Here is another variant playground. It is by far more efficient in terms of both speed and memory than other answers. If you want to run benchmarks here they are benchmarks.

func Chunks(s string, chunkSize int) []string {
    if chunkSize >= len(s) {
        return []string{s}
    }
    var chunks []string
    chunk := make([]rune, chunkSize)
    len := 0
    for _, r := range s {
        chunk[len] = r
        len++
        if len == chunkSize {
            chunks = append(chunks, string(chunk))
            len = 0
        }
    }
    if len > 0 {
        chunks = append(chunks, string(chunk[:len]))
    }
    return chunks
}