CODEWITHSUNDEEP
kotlin
asanelder
asanelder

Reputation: 51

kotlin: how to use the Intermediate collection when do stream operations

for example

val coordinates: Array<IntArray> = [[1, 2], [1, 3], [1, 4]]

coordinates
   .map {it[0]} 
   .all {it == x[0]}

x means the map result of coordinates. I want use it in the 'all' step, how to do that?

Upvotes: 1

Views: 67

Answers (2)

Sweeper
Sweeper

Reputation: 270995

If I understand correctly, you can just declare a val called x:

val x = coordinates.map { it[0] }
val result = x.all { it == x[0] }

Or if you want to do it in one expression, you can use the scope function run or let:

val result = coordinates.map { it[0] }.run {
    all { it == this[0] }
}

or:

val result = coordinates.map { it[0] }.let { x ->
    x.all { it == x[0] }
}

Though, if you just want to check if the whole list has exactly one unique value, I think this is more readable:

val result = coordinates.map { it[0] }.distinct().size == 1

The above doesn't short-circuit like all. A shortcircuiting version would need Sequence:

val result = coordinates
    .asSequence()
    .map { it[0] }
    .distinct().take(2).count() == 1

Upvotes: 1

Ivo
Ivo

Reputation: 23164

You could just write this

coordinates
   .map {it[0]} 
   .all {it == coordinates[0][0]}

Or if you don't want to directly refer to coordinates again, maybe insert a let like

coordinates
    .map { it[0] }
    .let { x -> x.all { it == x[0] } }

Although for your specific use case I probably would just do

coordinates
    .all { it[0] == coordinates[0][0] }

Upvotes: 1

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