All the integer functions in math/rand generate non-negative numbers.
rand.Int() int // [0, MaxInt]
rand.Int31() int32 // [0, MaxInt32]
rand.Int31n(n int32) int32 // [0, n)
rand.Int63() int64 // [0, MaxInt64]
rand.Int63n(n int64) int64 // [0, n)
rand.Intn(n int) int // [0, n)
I would like to generate random numbers in the range [-m, n). In other words, I would like to generate a mix of positive and negative numbers.
I found this example at Go Cookbook, which is equivalent to rand.Range(min, max int) (if that function existed):
rand.Intn(max - min) + min
As to prevent repeating min and max over and over again, I suggest to switch range and random in thinking about it. This is what I found to work as expected:
package main
import (
"fmt"
"math/rand"
)
// range specification, note that min <= max
type IntRange struct {
min, max int
}
// get next random value within the interval including min and max
func (ir *IntRange) NextRandom(r* rand.Rand) int {
return r.Intn(ir.max - ir.min +1) + ir.min
}
func main() {
r := rand.New(rand.NewSource(55))
ir := IntRange{-1,1}
for i := 0; i<10; i++ {
fmt.Println(ir.NextRandom(r))
}
}
The solution you found in the Cookbook misses to exactly specify how min and max work, but of course it meets your specification ([-min, max)). I decided to specify the range as a closed interval ([-min, max], than means its borders are included in the valid range). Compared to my understanding of the Cookbook description:
gives you that random number within any two positive numbers that you specify (in this case, 1 and 6).
(which can be found below the code snippet in the Golang Cookbook)
the Cookbook implementation is off by one (which of course brings it in good company with lots of program that are helpful at first glance).
A small utility I wrote for generating random slices(very much like python range)
Code - https://github.com/alok87/goutils/blob/master/pkg/random/random.go
import "github.com/alok87/goutils/pkg/random"
random.RangeInt(2, 100, 5)
[3, 10, 30, 56, 67]
This will generate random numbers within given range [a, b]
rand.Seed(time.Now().UnixNano())
n := a + rand.Intn(b-a+1)