CODEWITHSUNDEEP
javafunctional-programmingkotlin
Ali Urz
Ali Urz

Reputation: 107

Change a list to map in Kotlin while customize this convert

var listOfNums = listOf(1,9,8,25,5,44,7,95,9,10)
var mapOfNums = listOfNums.map { it to it+1 }.toMap()
println(mapOfNums)

result

{1=2, 9=10, 8=9, 25=26, 5=6, 44=45, 7=8, 95=96, 10=11}

while I need this result, it adds contents of next element to the current element while I need to map current element to next element

my goal result

{1=9, 8=25, 5=44, 7=59, 9=10}

Upvotes: 3

Views: 562

Answers (3)

Arsala Bangash
Arsala Bangash

Reputation: 439

We can step over every second index and map listOfNums[it] to listOfNums[it+1]

val listOfNums = listOf(1,9,8,25,5,44,7,95,9,10)
val mapOfNums = mutableMapOf<Int, Int>()
(listOfNums.indices step 2).forEach {
    mapOfNums[listOfNums[it]] = listOfNums[it + 1]
}
println(mapOfNums)

EDIT: Another better solution suggested by ephemient: 

 (1..listOfNums.lastIndex step 2).associate { listOfNums[it - 1] to listOfNums[it] }

Elegant!

Upvotes: 1

marstran
marstran

Reputation: 27971

For Kotlin 1.1:

First, use zip to create a list with adjacent pairs. Then you drop every other pair, before converting it to a Map. Like this:

val list = listOf(1,9,8,25,5,44,7,95,9,10)
val mapOfNums = list.zip(list.drop(1))
                    .filterIndexed { index, pair -> index % 2 == 0 }
                    .toMap())

For Kotlin 1.2:

Kotlin 1.2 brings the chunked function which will make this a bit easier. This function divides the list up in sublists of the given length. You can then do this:

val list = listOf(1,9,8,25,5,44,7,95,9,10)
val mapOfNums = list.chunked(2).associate { (a, b) -> a to b }

Upvotes: 6

Kevin Robatel
Kevin Robatel

Reputation: 8386

With the help of RxJava

import io.reactivex.Observable

...

val listOfNums = listOf(1,9,8,25,5,44,7,95,9,10)
val mapOfNums = Observable.fromIterable(listOfNums)
        .buffer(2)
        .map { it[0] to it[1] }
        .collect(
                { mutableMapOf<Int, Int>() },
                { map: MutableMap<Int, Int>, (first, second) -> map.put(first, second) }
        )
        .blockingGet()
println(mapOfNums)
// {1=9, 8=25, 5=44, 7=95, 9=10}

Upvotes: 1

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