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A Go function to render a number to a string based on the following user-specified criteria: thousands separator, decimal separator, decimal precision. I didn't feel it was worth to publish a library just for this piece of code, hence the snippet. Feel free to reuse as you wish.

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render_number.go
Go
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/*
 
Author: https://github.com/gorhill
Source: https://gist.github.com/gorhill/5285193
 
A Go function to render a number to a string based on
the following user-specified criteria:
 
* thousands separator
* decimal separator
* decimal precision
 
Usage: s := RenderFloat(format, n)
 
The format parameter tells how to render the number n.
 
http://play.golang.org/p/LXc1Ddm1lJ
 
Examples of format strings, given n = 12345.6789:
 
"#,###.##" => "12,345.67"
"#,###." => "12,345"
"#,###" => "12345,678"
"#\u202F###,##" => "12 345,67"
"#.###,###### => 12.345,678900
"" (aka default format) => 12,345.67
 
The highest precision allowed is 9 digits after the decimal symbol.
There is also a version for integer number, RenderInteger(),
which is convenient for calls within template.
 
I didn't feel it was worth to publish a library just for this piece
of code, hence the snippet. Feel free to reuse as you wish.
 
*/
 
import (
"math"
"strconv"
)
 
var renderFloatPrecisionMultipliers = [10]float64{
1,
10,
100,
1000,
10000,
100000,
1000000,
10000000,
100000000,
1000000000,
}
 
var renderFloatPrecisionRounders = [10]float64{
0.5,
0.05,
0.005,
0.0005,
0.00005,
0.000005,
0.0000005,
0.00000005,
0.000000005,
0.0000000005,
}
 
func RenderFloat(format string, n float64) string {
// Special cases:
// NaN = "NaN"
// +Inf = "+Infinity"
// -Inf = "-Infinity"
if math.IsNaN(n) {
return "NaN"
}
if n > math.MaxFloat64 {
return "Infinity"
}
if n < -math.MaxFloat64 {
return "-Infinity"
}
 
// default format
precision := 2
decimalStr := "."
thousandStr := ","
positiveStr := ""
negativeStr := "-"
 
if len(format) > 0 {
// If there is an explicit format directive,
// then default values are these:
precision = 9
thousandStr = ""
 
// collect indices of meaningful formatting directives
formatDirectiveChars := []rune(format)
formatDirectiveIndices := make([]int, 0)
for i, char := range formatDirectiveChars {
if char != '#' && char != '0' {
formatDirectiveIndices = append(formatDirectiveIndices, i)
}
}
 
if len(formatDirectiveIndices) > 0 {
// Directive at index 0:
// Must be a '+'
// Raise an error if not the case
// index: 0123456789
// +0.000,000
// +000,000.0
// +0000.00
// +0000
if formatDirectiveIndices[0] == 0 {
if formatDirectiveChars[formatDirectiveIndices[0]] != '+' {
panic("RenderFloat(): invalid positive sign directive")
}
positiveStr = "+"
formatDirectiveIndices = formatDirectiveIndices[1:]
}
 
// Two directives:
// First is thousands separator
// Raise an error if not followed by 3-digit
// 0123456789
// 0.000,000
// 000,000.00
if len(formatDirectiveIndices) == 2 {
if (formatDirectiveIndices[1] - formatDirectiveIndices[0]) != 4 {
panic("RenderFloat(): thousands separator directive must be followed by 3 digit-specifiers")
}
thousandStr = string(formatDirectiveChars[formatDirectiveIndices[0]])
formatDirectiveIndices = formatDirectiveIndices[1:]
}
 
// One directive:
// Directive is decimal separator
// The number of digit-specifier following the separator indicates wanted precision
// 0123456789
// 0.00
// 000,0000
if len(formatDirectiveIndices) == 1 {
decimalStr = string(formatDirectiveChars[formatDirectiveIndices[0]])
precision = len(formatDirectiveChars) - formatDirectiveIndices[0] - 1
}
}
}
 
// generate sign part
var signStr string
if n >= 0.000000001 {
signStr = positiveStr
} else if n <= -0.000000001 {
signStr = negativeStr
n = -n
} else {
signStr = ""
n = 0.0
}
 
// split number into integer and fractional parts
intf, fracf := math.Modf(n + renderFloatPrecisionRounders[precision])
 
// generate integer part string
intStr := strconv.Itoa(int(intf))
 
// add thousand separator if required
if len(thousandStr) > 0 {
for i := len(intStr); i > 3; {
i -= 3
intStr = intStr[:i] + thousandStr + intStr[i:]
}
}
 
// no fractional part, we can leave now
if precision == 0 {
return signStr + intStr
}
 
// generate fractional part
fracStr := strconv.Itoa(int(fracf * renderFloatPrecisionMultipliers[precision]))
// may need padding
if len(fracStr) < precision {
fracStr = "000000000000000"[:precision-len(fracStr)] + fracStr
}
 
return signStr + intStr + decimalStr + fracStr
}
 
func RenderInteger(format string, n int) string {
return RenderFloat(format, float64(n))
}
~LICENSE
1 2 3 4 5 6 7 8 9 10 11 12 13
DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE
Version 2, December 2004
 
Copyright (C) 2004 Sam Hocevar <sam@hocevar.net>
 
Everyone is permitted to copy and distribute verbatim or modified
copies of this license document, and changing it is allowed as long
as the name is changed.
 
DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE
TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
 
0. You just DO WHAT THE FUCK YOU WANT TO.

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