Format a float to n decimal places and no trailing zeros

Question

I want to display a float with the entire integer part and up to two decimals for the fractional part, without trailing zeros.

http://play.golang.org/p/mAdQl6erWX:

// Desired output: 
// "1.9"
// "10.9"
// "100.9"

fmt.Println("2g:")
fmt.Println(fmt.Sprintf("%.2g", 1.900)) // outputs "1.9"
fmt.Println(fmt.Sprintf("%.2g", 10.900)) // outputs "11"
fmt.Println(fmt.Sprintf("%.2g", 100.900)) // outputs "1e+02"

fmt.Println("\n2f:")
fmt.Println(fmt.Sprintf("%.2f", 1.900)) // outputs "1.90"
fmt.Println(fmt.Sprintf("%.2f", 10.900)) // outputs "10.90"
fmt.Println(fmt.Sprintf("%.2f", 100.900)) // outputs "100.90"

Formatting with 2g has the problem that it starts rounding when the integer increases order of magnitudes. Also, it sometimes displays numbers with an e.

Formatting with 2f has the problem that it will display trailing zeros. I could write a post-processing function that removes trailing zeros, but I rather do this with Sprintf.

Can this be done in a generic way using Sprintf?
If not, what's a good way to do this?

In `%.Ng` N is a total number of digits, not a precision. Unfortunately I don't think you can implement your requirements using `Sprintf` only. — kostya, Jul 08 '15 at 11:08

score 82 · Accepted Answer · answered Nov 11 '16 at 19:56

82

strconv.FormatFloat(10.900, 'f', -1, 64)

This will result in 10.9.

The -1 as the third parameter tells the function to print the fewest digits necessary to accurately represent the float.

See here: https://golang.org/pkg/strconv/#FormatFloat

answered Nov 11 '16 at 19:56

Eric E.

836
7
2

16

This does not strictly solve their problem, because they want a precision of 2 points. – devoxel Oct 13 '17 at 13:11

ferhatelmas · Answer 2 · 2015-07-08T11:27:54.460

7

Not sure for Sprintf but to make it worked. Just trim right, first 0 then ..

fmt.Println(strings.TrimRight(strings.TrimRight(fmt.Sprintf("%.2f", 100.900), "0"), ".")) // 100.9
fmt.Println(strings.TrimRight(strings.TrimRight(fmt.Sprintf("%.2f", 100.0), "0"), ".")) // 100

edited Jul 08 '15 at 11:27

answered Jul 08 '15 at 10:13

ferhatelmas

3,818
1
21
25

score 5 · Answer 3 · answered Jan 17 '19 at 21:15

5

I used the below func to achive the same:

//return 45.00 with "45" or 45.50 with "45.5"
func betterFormat(num float32) string {
    s := fmt.Sprintf("%.4f", num)
    return strings.TrimRight(strings.TrimRight(s, "0"), ".")
}

answered Jan 17 '19 at 21:15

Hamid Karimi

615
1
8
12

1

@SergeyPonomarev that won't work. In case the number is `10.0`, it will become just `1` – FirstOne Feb 15 '23 at 17:57
@FirstOne you are right, I removed my comment to avoid confusion – Sergey Ponomarev Feb 16 '23 at 19:50

Sadegh · Answer 4 · 2022-05-11T08:14:03.863

1

Use the below function to format and control the number of digits.

func FormatFloat(num float64, prc int) string {
    var (
        zero, dot = "0", "."

        str = fmt.Sprintf("%."+strconv.Itoa(prc)+"f", num)
    )
    
    return strings.TrimRight(strings.TrimRight(str, zero), dot)
}

Here is an example:

// Converts 18.24100100 to 18.24
fmt.Println(FormatFloat(18.24100100, 2))

edited May 11 '22 at 08:14

answered Jun 13 '20 at 18:34

Sadegh

13
5

Sergey Ponomarev · Answer 5 · 2023-02-17T13:21:42.670

We must trim those zeros ourselves. We can use TrimRight(priceStr, "0.") but I wrote more faster trimmer

func formatPrice(price float32) string {
    // truncate to 3 digits after point
    priceStr := strconv.FormatFloat(float64(price), 'f', 3, 32)
    priceStr = trimFloatTrailingZeros(priceStr)
    return priceStr
}

// trimFloatTrailingZeros the FormatFloat add padding zeros e.g. 20.900 to 20.9 or 10.0 to 10
// Note: the number must contain the decimal dot e.g. as result of format
func trimFloatTrailingZeros2(s []byte) []byte {
    i := len(s) - 1
    for ; i >= 1; i-- {
        digit := s[i]
        if digit == '0' {
        } else {
            if digit == '.' {
                return s[:i]
            } else {
                return s[:i+1]
            }
        }
    }
    return s
}

Format a float to n decimal places and no trailing zeros

5 Answers5