How to divide String by regex e g ` AAA foo BBB bar CCC ` to ` AAA foo BBB bar CCC ` if regex is ` `

A normal split operation won t do becasue the separator is usually not included in the result you could do something like this for your specific case ```fun customSplit input String List lt String gt return ^ + toRegex findAll input flatMap match gt sequence yield match groupValues 1 match groupValues 2 takeIf it isNotBlank let yield it toList ```

zero width lookahead lookbehind ``` AAA foo BBB bar CCC split = | lt = toRegex ``` not all JS RegExp engines support lookbehind though

Here is a different approach that takes any regex ```fun customSplit input String regex Regex List lt String gt var nextSliceIndex = 0 val result = regex findAll input fold mutableListOf lt String gt result match gt val range = match range result += input slice nextSliceIndex until range first result += input slice range nextSliceIndex = range last + 1 result if nextSliceIndex lt input length result += input substring nextSliceIndex return result ```

How to divide String by regex e g ` AAA foo BBB bar CCC ` to kotlinlang #getting-started

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ken_kentan

09/14/2020, 9:18 AM

How to divide String by regex? e.g.

"AAA{foo}BBB{bar}CCC"

["AAA", "{foo}", "BBB", "{bar}", "CCC"]

if regex is

\{.*?}

Tobias Berger

09/14/2020, 9:40 AM

A normal split operation won't do becasue the separator is usually not included in the result. you could do something like this for your specific case:

fun customSplit(input: String): List<String> {
    return "([^{]+)(\\{.*?})?".toRegex().findAll(input).flatMap { match ->
        sequence {
            yield(match.groupValues[1])
            match.groupValues[2].takeIf { it.isNotBlank() }?.let { yield(it) }
        }
    }.toList()
}

ephemient

09/14/2020, 9:52 AM

zero-width lookahead/lookbehind:

"AAA{foo}BBB{bar}CCC".split("""(?=\{)|(?<=})""".toRegex())

(not all JS RegExp engines support lookbehind though)

Tobias Berger

09/14/2020, 9:55 AM

good idea, didn't think of this. I don't know the case where this will be used but it is probaby sufficient, although it will just split before each

and after each

ephemient

09/14/2020, 9:56 AM

https://caniuse.com/js-regexp-lookbehind

yeah, both our solutions have some edge cases on different inputs

(what should happen on

{{{foo}

? yours drops the leading

, mine separates them)

ken_kentan

09/14/2020, 9:59 AM

It seems difficult to support some edge case like

AAA{foo}BBB{bar}CCC}DDD{EEE

etc..

Tobias Berger

09/14/2020, 10:00 AM

sure, mine isn't perfect at all, it was just my first idea. Both approaches require some regex-skills if you want to customize

👍 1

Here is a different approach that takes any regex

fun customSplit(input: String, regex: Regex): List<String> {
    var nextSliceIndex = 0
    val result = regex.findAll(input).fold(mutableListOf<String>()) { result, match ->
        val range = match.range
        result += input.slice(nextSliceIndex until range.first)
        result += input.slice(range)
        nextSliceIndex = range.last + 1
        result
    }
    if (nextSliceIndex < input.length) {
        result += input.substring(nextSliceIndex)
    }
    return result
}

👀 1

stephanmg

09/14/2020, 10:02 AM

@ephemient you can use capture groups to handle your edge case

ken_kentan

09/14/2020, 10:13 AM

I will try to use Tobias's approach! Thank you everyone!

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