how to get index list in arrayList filter

Question

I want to get index list as follows.

val a = booleanArrayOf(true,false,true,false)

above code, True number is two. -> indexList = {0, 2} how to get indexList in Kotlin.

Todd · Accepted Answer · 2018-06-07 01:23:41Z

34

You could use mapIndexed() to get the index and the value of each element, convert to either the index or null, and then remove the nulls...

val b: List<Int> = a.mapIndexed { i, b -> if (b) i else null }.filterNotNull().toList()

Another way would be to use the withIndex() function, filter the values that are true, and map the resulting pairs to the index value. This might be a bit clearer.

val c: List<Int> = a.withIndex().filter { it.value }.map { it.index }

edited Jun 7, 2018 at 1:23

answered Jun 7, 2018 at 1:08

Todd

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varotariya vajsi Over a year ago

Thanks @Todd, I am using as below example

val indexList: List<Int> = yourList.withIndex().filter {                 (!it.value.your_custom_object!!.keyName.equals("") && it.value.your_custom_object!!.keyName!!.equals(                     "some_value", ignoreCase = true                 ))             }.map { it.index }

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