Golang : Round float to precision example
Just an add on for my previous tutorial on how to round up or down a float number. For this short tutorial, we will learn how to round float numbers to certain precision.
Instead of using
fmt.Printf("%0.2f \n", f)
fmt.Printf("%0.2f \n", Round(f)) // round half
fmt.Printf("%0.2f \n", RoundUp(f, 2)) // change 2 to 5 will have no effect
fmt.Printf("%0.2f \n", RoundDown(f, 3)) // change 3 to 4 will have no effect
which will output the precision up to 2 decimal point no matter how you instruct the Round, RoundUp and RoundDown functions.
This is because of fmt.Printf(%0.2\n)
will always overrule the final display format.
To fix this problem or to display the precision properly, you will have to use fmt.Println()
instead.
var f float64 = 123.123456
fmt.Printf("%0.2f \n", f)
fmt.Println(Round(f)) // round half
fmt.Println(RoundUp(f, 4)) // up to precision 4
fmt.Println(RoundDown(f, 4)) // up to precision 4
Output :
123.12
123
123.1235
123.1234
Here's the full code :
package main
import (
"fmt"
"math"
)
func Round(input float64) float64 {
if input < 0 {
return math.Ceil(input - 0.5)
}
return math.Floor(input + 0.5)
}
func RoundUp(input float64, places int) (newVal float64) {
var round float64
pow := math.Pow(10, float64(places))
digit := pow * input
round = math.Ceil(digit)
newVal = round / pow
return
}
func RoundDown(input float64, places int) (newVal float64) {
var round float64
pow := math.Pow(10, float64(places))
digit := pow * input
round = math.Floor(digit)
newVal = round / pow
return
}
func main() {
var f float64 = 123.123456
fmt.Printf("%0.2f \n", f)
fmt.Println(Round(f)) // round half
fmt.Println(RoundUp(f, 4))
fmt.Println(RoundDown(f, 4))
}
Reference :
By Adam Ng
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