Change the positions of list elements with some conditions

Question

I have a list of strings like this :-

listOf("abc", "a", "bb", "aa", "aaa", "bb", "a")

I want an output like this :-

listOf("a", "a", "aa", "bb", "bb", "aaa", "abc")

First I want to sort list by length and then again sort that length group by letters.

I tried below code so far

fun main() {
    val result = listOf("abc", "a", "bb", "aa", "aaa", "bb", "a").groupBy { it.length }
    val valueList = ArrayList(result.values).flatMap { it.toList() }
    println(valueList)
}

But the result I got is like below

[abc, aaa, a, a, bb, aa, bb]

After @Sergey Lagutin's duplication comment I also tried

val sortedList = a.sortedWith(compareBy { it.length })

Which is not returning the desired result

Possible duplicate of [How to sort based on/compare multiple values in Kotlin?](https://stackoverflow.com/questions/33640864/how-to-sort-based-on-compare-multiple-values-in-kotlin) — Sergii Lagutin, Feb 06 '19 at 09:46
The example from [here](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.comparisons/natural-order.html) should work. — TiiJ7, Feb 06 '19 at 09:52
The original problem in the code was that `groupBy` function returns an unsorted Map, so `result.values` has to be sorted by key values first. There is no need to wrap `result.values` with ArrayList — Eugene Petrenko, Feb 06 '19 at 10:03

score 2 · Accepted Answer · answered Feb 06 '19 at 10:27

2

val a = listOf("abc", "a", "bb", "aa", "aaa", "bb", "a")
a.sortedWith(compareBy({ it.length }, { it })) // [a, a, aa, bb, bb, aaa, abc]

answered Feb 06 '19 at 10:27

Sergii Lagutin

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score 1 · Answer 2 · answered Feb 06 '19 at 10:35

You can try this way

val yourList = listOf("abc", "a", "bb", "aa", "aaa", "bb", "a")
val yourSortedList = yourList.sorted().sortedBy { it.length }

sorted will sort you list according to their natural sort order. In this case it will be alphabetic order.
With sortyBy you precise that the sort order is the length of your string.

Result [a, a, aa, bb, bb, aaa, abc]

Eugene Petrenko · Answer 3 · 2019-02-06T21:15:14.447

0

Use sortedWith function on the collection

val a = listOf("abc", "a", "bb", "aa", "aaa", "bb", "a")
val b = a.sortedWith(compareBy({ it.length }, { it }))
println(b)

edited Feb 06 '19 at 21:15

answered Feb 06 '19 at 10:00

Eugene Petrenko

4,874
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`thenComparing` requires minimum api level 24 – Mahesh Babariya Feb 06 '19 at 10:07
You may pass several lambdas to the `compareBy` function. I'll update the example. – Eugene Petrenko Feb 06 '19 at 21:13

Change the positions of list elements with some conditions

3 Answers3