How to generate a sequence of numbers

Question

I want to generate a sequence of numbers in Go but I can't find any built-in functions for this.
Basically I want the equivalent of PHP's range function in Golang:

array range ( mixed $start , mixed $end [, number $step = 1 ] )

It would be useful when creating a slice/array of numeric types and you want to populate/initialize it with a numeric sequence.

Solution 1

There is no equivalent to PHP's range in the Go standard library. You have to create one yourself. The simplest is to use a for loop:

func makeRange(min, max int) []int {
    a := make([]int, max-min+1)
    for i := range a {
        a[i] = min + i
    }
    return a
}

Using it:

a := makeRange(10, 20)
fmt.Println(a)

Output (try it on the Go Playground):

[10 11 12 13 14 15 16 17 18 19 20]

Also note that if the range is small, you can use a composite literal:

a := []int{1, 2, 3}
fmt.Println(a) // Output is [1 2 3]

Solution 2

1- You may use:

//Create a slice containing a range of elements.
//
//  start: First value of the sequence.
//  end:   The sequence is ended upon reaching the end value.
//  step:  step will be used as the increment between elements in the sequence.
//         step should be given as a positive number.
//
//Return Values: Returns a slice of elements from start to end, inclusive.
func NewSlice(start, end, step int) []int {
    if step <= 0 || end < start {
        return []int{}
    }
    s := make([]int, 0, 1+(end-start)/step)
    for start <= end {
        s = append(s, start)
        start += step
    }
    return s
}

Try it on The Go Playground:

package main

import "fmt"

//Create a slice containing a range of elements.
//
//  start: First value of the sequence.
//  end:   The sequence is ended upon reaching the end value.
//  step:  step will be used as the increment between elements in the sequence.
//         step should be given as a positive number.
//
//Return Values: Returns a slice of elements from start to end, inclusive.
func NewSlice(start, end, step int) []int {
    if step <= 0 || end < start {
        return []int{}
    }
    s := make([]int, 0, 1+(end-start)/step)
    for start <= end {
        s = append(s, start)
        start += step
    }
    return s
}

func main() {
    s := []int{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
    fmt.Println(s) // [0 1 2 3 4 5 6 7 8 9]

    fmt.Println(NewSlice(10, 19, 1))  // [10 11 12 13 14 15 16 17 18 19]
    fmt.Println(NewSlice(10, 28, 2))  // [10 12 14 16 18 20 22 24 26 28]
    fmt.Println(NewSlice(-10, -1, 1)) // [-10 -9 -8 -7 -6 -5 -4 -3 -2 -1]
}

---

2- You may use:

// Returns a slice of elements with exact count.
// step will be used as the increment between elements in the sequence.
// step should be given as a positive, negative or zero number.
func NewSlice(start, count, step int) []int {
    s := make([]int, count)
    for i := range s {
        s[i] = start
        start += step
    }
    return s
}

Try it on The Go Playground:

package main

import "fmt"

func NewSlice(start, count, step int) []int {
    s := make([]int, count)
    for i := range s {
        s[i] = start
        start += step
    }
    return s
}

func main() {
    s := []int{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
    fmt.Println(s) // [0 1 2 3 4 5 6 7 8 9]

    fmt.Println(NewSlice(10, 10, 1))  // [10 11 12 13 14 15 16 17 18 19]
    fmt.Println(NewSlice(10, 10, 2))  // [10 12 14 16 18 20 22 24 26 28]
    fmt.Println(NewSlice(-1, 10, -1)) // [-1 -2 -3 -4 -5 -6 -7 -8 -9 -10]
    fmt.Println(NewSlice(20, 10, 0))  // [20 20 20 20 20 20 20 20 20 20]
}

Solution 3

package main

import "fmt"

func main() {

  var a [11]int
  for i := 1; i < len(a); i++ {
    a[i] = i
  }
  
  fmt.Print(a)
}

You will get:

[0 1 2 3 4 5 6 7 8 9 10]