Replace occurence in a String in Kotlin - list

Question

I have two list of Strings. Now I want to replace every occurence of a word in the first list at index i with a word in the second list at index i of a sentence.
So if I have
list a=("am","I","my")
and
list b=("are","You","your")
I want the sentence "I am an amateur"
to become "You are an amateur"
What is cleanest way to do that in Kotlin (without for loop)?

Answer 1

First split the string to a list of its words and then map each word if it exists in list a to the corresponding word in list b. Finally rejoin the string:
val a= listOf("am","I","my")
val b= listOf("are","You","your")
val str = "I am an amateur"
val new = str
.split("\\s+".toRegex())
.map { val i = a.indexOf(it); if (i < 0) it else b[i] }
.joinToString(" ")
Another way of doing the same thing is:
var new = " $str "
a.forEachIndexed { i, s -> new = new.replace(" $s ", " ${b[i]} ") }
new = new.trim()
although this is closer to a for loop.

Answer 2

I assume there is no punctuation, all whitespaces are spaces and so on.
val m = a.zip(b).toMap()
return s.split(' ').joinToString(" ") { m[it] ?: it }
First you create a map m for more efficient... mapping. Then
Split the string to get a list of words
Map all words: if m contains the word, then return the value (i.e. the replacement), otherwise return the original word (since we shouldn't replace it).
Join all words, separate them by spaces.

Answer 3

You can use the regular expression \b\w+\b to match words in a sentence and then call replace function with the lambda that provides a replacement string for each match:
val input = "I am an amateur, alas."
val wordsToReplace = listOf("I", "am", "my")
val wordsReplaceWith = listOf("You", "are", "your")
val wordRegex = """\b\w+\b""".toRegex()
val result = wordRegex.replace(input) { match ->
val wordIndex = wordsToReplace.indexOf(match.value)
if (wordIndex >= 0) wordsReplaceWith[wordIndex] else match.value
}
println(result)
If there are a lot of word in your lists, it makes sense to build a map of them to speed up searches:
val replaceMap = (wordsToReplace zip wordsReplaceWith).toMap()
val result = wordRegex.replace(input) { match ->
replaceMap[match.value] ?: match.value
}

Answer 4

I think the simplest way is to create a set of regex you want and replace the string by iteration. Let's say you want to replace the word "am", your regex will be "\bam\b". You can use "(?i)\bam\b" if you want it not to be case sensitive. To make "I am an amateur" to "You are an amateur"
val replacements = setOf("\\bam\\b" to "are",
"\\bI\\b" to "You",
"\\bmy\\b" to "your")
replacements.forEach {
str = str.replace(Regex(it.first), it.second)
}