How to change different substrings in a string?

Question

I have a file with a certain number of lines. I need to find all double letters and change the second letter to the one that corresponds to it in the map.
Case of replaced letters should be kept.
Example:
"kotlIn is a functional programming Language"
should become
"kotlYn is a functionol programmyng Longuage"

fun changeChar(inputFileName: String, outputFileName: String) {
    val outputStream = File(outputFileName).bufferedWriter()
    val charsRegex = "([klmn][aei])".toRegex(setOf(RegexOption.IGNORE_CASE))
    val validChars = mapOf('a' to 'o', 'e' to 'u', 'i' to 'y')
    File(inputFileName).forEachLine { line ->
        val sb = StringBuilder(line).replace(charsRegex, /*here is my difficulty*/)
        outputStream.write(sb)
        outputStream.newLine()
    }
    outputStream.close()
}

I spent many hours, but could not find solutions on the Internet and the standard Kotlin library.

hotkey · Accepted Answer · 2019-01-30 23:14:30Z

1

Another idiomatic solution would be to transform the matched string using the replace(...) { ... } overload that accepts a lambda to handle each MatchResult:

val charsRegex = "[klmn][aei]".toRegex(RegexOption.IGNORE_CASE)
val validChars = mapOf('a' to 'o', 'e' to 'u', 'i' to 'y')

val result = line.replace(charsRegex) {
    val vowel = it.value[1]
    val validLetter = validChars.getValue(vowel.toLowerCase())
    val validCaseLetter = if (vowel.isLowerCase()) validLetter else validLetter.toUpperCase()
    it.value.take(1) + validCaseLetter
}

^{(runnable sample)}

answered Jan 30, 2019 at 23:14

hotkey

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Comments

forpas · Accepted Answer · 2019-01-30 17:11:23Z

1

Without any regex:

val validChars = mapOf('a' to 'o', 'e' to 'u', 'i' to 'y')
val chars = validChars.plus(validChars.map { it.key.toUpperCase() to it.value.toUpperCase() }.toMap())

var pattern = "klmn"
pattern = pattern.plus(pattern.toUpperCase())

val str = "kotlIn is a functional programming Language"
val result = str.mapIndexed { i, c ->
    if (i > 0) { if (pattern.contains(str[i -1])) chars.getOrDefault(c, c) else c } else c
}.joinToString("")
println(result)

will print:

kotlYn is a functionol programmyng Longuage

edited Jan 30, 2019 at 17:11

answered Jan 30, 2019 at 16:31

forpas

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1 Comment

rost Over a year ago

This is not what i need. I need the value to change only at the letter after klmn. Like in my pattern "([klmn][aei])". And then each aei symbol was replaced with the corresponding one in the map val validChars = mapOf('a' to 'o', 'e' to 'u', 'i' to 'y')

stack0114106 · Accepted Answer · 2019-01-30 21:01:22Z

Try this.

fun main(args: Array<String>) {
    val str = "kotlIn is a functional programming Language"
    val validChars = mapOf("a" to "o", "e" to "u", "i" to "y" )
    val charsRegex = "(?=(.))([klmn][aei])(?<=(.))".toRegex(setOf(RegexOption.IGNORE_CASE))
    val found = charsRegex.findAll(str)
    var newStr= str
    found.forEach { f ->
        val m = f.value.toLowerCase()
        val idx = f.range
        val k = m.substring(1)
        val repStr = m.substring(0,1) + validChars.get(k)?.toUpperCase()
        newStr= newStr.replaceRange(idx,repStr)
       // println("$m found at indexes: $idx  ${validChars.get(k)} ${newStr}" )
     }
    println( "NewStr = ${newStr}")
}

Prints

NewStr = kotlYn is a functionOl programmYng lOnguage

PS: I'm not that good at Kotlin, but I think you can tweak it a little to get the accurate results.

Willi Mentzel · Accepted Answer · 2019-01-31 00:58:47Z

I would use replace which takes a transform lambda as hotkey proposed as well. But I would change the regex to have two groups.

The first group is a positive lookbehind which means that it will be matched but not captured, since the first letter does not have to be replaced
The second group will be captured, since the second letter has to be replaced by another character

Code:

fun replaceInvalidPairs(line: String): String {
    val charsRegex = "(?<=[klmn])([aei])".toRegex(setOf(RegexOption.IGNORE_CASE))
    val validChars = mapOf('a' to 'o', 'e' to 'u', 'i' to 'y')

    return charsRegex.replace(line) {
        val secondLetter = it.groupValues.first().first()
        val replacement = validChars[secondLetter.toLowerCase()]!!
        (if (secondLetter.isUpperCase()) replacement.toUpperCase() else replacement).toString()
    }
}

Result:

kotlYn is a functionol programmyng Longuage

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