Distinct not working for ArrayList in Kotlin

Question

I am trying to remove duplicates from an ArrayList in Kotlin. First of all I am getting a sortedNews from somewhere else and then I am adding it to the list called newsItems and then I am trying to remove the duplicates but the duplicates are still there. What am I doing wrong here

sortedNewsItems = nsItems!!.sortedWith(compareByDescending({it!!.timeStamp}))
        newsItems?.addAll(sortedNewsItems!!)
        newsItems?.distinct()
        Log.e("first item name ",sortedNewsItems?.get(0)?.title)
        recyclerView.adapter.notifyDataSetChanged()

Not sure completely but newsItems?.distinct() returns new instance of collection. — oreh
– oreh, Commented Jun 8, 2018 at 14:47

yole · Accepted Answer · 2018-06-08 14:47:43Z

19

distinct does not remove duplicates from the collection, it returns a new collection with duplicates removed. You're ignoring the return value of distinct, so the call has no effect.

answered Jun 8, 2018 at 14:47

yole

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3 Comments

Matheus Ribeiro Over a year ago

May you please share your solution?

M Moersalin Over a year ago

@MatheusRibeiro you should use the return value val newList = items.distinct()

Matheus Ribeiro Over a year ago

@MMoersalin Yeah, I was too much of a newbie to understand that LOL

Simon · Accepted Answer · 2021-02-19 12:23:18Z

3

The best way would be to, instead of addAll use the function union

val firstList: ArrayList = arrayListOf(1, 2, 3, 4)
val secondList: ArrayList = arrayListOf(1, 5, 6, 7, 8)

val addAllList = firstList.addAll(secondList) //1,2,3,4,1,5,6,7,8
val unionList = firstList.union(secondList) //1,2,3,4,5,6,7,8

union - Returns a set containing all distinct elements from both collections.

The returned set preserves the element iteration order of the original array. Those elements of the other collection that are unique are iterated in the end in the order of the other collection.

To get a set containing all elements that are contained in both collections use intersect.

answered Feb 19, 2021 at 12:23

Simon

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Comments

MohammadAli · Accepted Answer · 2020-08-05 10:11:45Z

0

Also you can try toSet()

val newItems = postList //postList id old list
newItems.addAll(_postList) // _postList is new list
postList = newItems.toSet().toMutableList()

answered Aug 5, 2020 at 10:11

MohammadAli

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