CODEWITHSUNDEEP
androiddictionarykotlinfilter
hagar Mohamad
hagar Mohamad

Reputation: 137

Kotlin filter method

I have a list of ids say of size 10 and I have another list of items I want an efficient way to remove items that match any of those 10 ids

  val list=items.filter { id== 1||id==3... and so on but in a more efficient way }

thanks in advance

Upvotes: 0

Views: 221

Answers (3)

hagar Mohamad
hagar Mohamad

Reputation: 137

You can use predicate and filterTo method

//list of things you don't want in your filtered list
 val listOfIds= listOf(312,264,309,297,233,262,149,156,214,350,316,315)
//a predicate used in filterTo function
  private val someFilteringCondition = { num: Int ->listOfIds.contains(num) }

//list that we will filter into (it will contains filtered list
private val filteredPublishers = mutableListOf<SegmentModel>()

 items.filterNotTo(filteredPublishers,someFilteringCondition )
                        adpater?.publishersChanged(it)

now filteredPublishers list constains items that doesn't have mentioned ids

Upvotes: 0

deHaar
deHaar

Reputation: 18568

In case you are dealing with a MutableList, you could modify it (or a copy of it) by using the methods removeAll or retainAll:

Keep all items in ids that are not present in removeIds:

fun main() {
    val ids = mutableListOf(20, 30, 40, 42, 50, 60)
    val removeIds = listOf(20, 30, 40, 50, 60)
    ids.retainAll { it !in removeIds }
    println(ids)
}

or remove all items from ids that are present in removeIds:

fun main() {
    val ids = mutableListOf(20, 30, 40, 42, 50, 60)
    val removeIds = listOf(20, 30, 40, 50, 60)
    ids.removeAll { it in removeIds }
    println(ids)
}

Both mains reduce ids to just [42] in these examples and output exactly that.

Unfortunately, this will not work on immutable Lists, you would have to make it a MutableList first, preferably by using toMutableList() or anything similar.

Upvotes: 1

Twistleton
Twistleton

Reputation: 2935

Returns a list containing all elements of the original collection except the elements contained in the given elements collection:

fun main() {
    val ids = listOf(20, 30, 40, 50, 60)
    val removeIds = listOf(30, 60)
    val result = ids - removeIds
    println(result)   // [20, 40, 50]
}

Or with substract:

val result = ids subtract removeIds

Upvotes: 4

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