How to replace occured strings with a counter in Go regexp?

Question

For example, in this sentence,

Let freedom ring from the mighty mountains of New York. Let freedom ring from the heightening Alleghenies of Pennsylvania. Let freedom ring from the snow-capped Rockies of Colorado. Let freedom ring from the curvaceous slopes of California.

how to replace "Let freedom" with

"[1] Let freedom", "[2] Let freedom2", and so on.

I searched the Go regexp package, failed to find anything related increase counter. (Only find the ReplaceAllStringFunc, but I don't know how to use it.)

Amit Joki · Accepted Answer · 2015-01-11 13:14:29Z

2

You need something like this

r, i := regexp.MustCompile("Let freedom"), 0
r.ReplaceAllStringFunc(input, func(m string) string {
   i += 1
   if i == 1 {
     return "[1]" + m 
   }
   return fmt.Sprintf("[%d] %s%d", i, m, i)
})

Make sure you've imported required packages.. The above works by using Let freedom as the regex and then using some conditions to return what is intended.

edited Jan 11, 2015 at 13:14

answered Jan 11, 2015 at 13:02

Amit Joki

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tumdum · Accepted Answer · 2015-01-11 13:09:05Z

0

You need to somehow share counter between successive calls to your function. One way to do this is to construct closure. You can do it this way:

package main

import (
    "fmt"
    "regexp"
)

func main() {
    str := "Let freedom ring from the mighty mountains of New York. Let freedom ring from the heightening Alleghenies of Pennsylvania. Let freedom ring from the snow-capped Rockies of Colorado. Let freedom ring from the curvaceous slopes of California."
    counter := 1
    repl := func(match string) string {
        old := counter
        counter++
        if old != 1 {
            return fmt.Sprintf("[%d] %s%d", old, match, old)
        }
        return fmt.Sprintf("[%d] %s", old, match)
    }
    re := regexp.MustCompile("Let freedom")
    str2 := re.ReplaceAllStringFunc(str, repl)
    fmt.Println(str2)
}

edited Jan 11, 2015 at 13:09

answered Jan 11, 2015 at 13:02

tumdum

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1 Comment

Nick Over a year ago

Thank you very much! +1 for your explanation on construct closure. Your code works well. I don't understand the if old != 1 { return fmt.Sprintf("[%d] %s%d", old, match, old) } part. So I removed it, the code still works.

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