CODEWITHSUNDEEP
scalafor-loopconcatenationyield
cemonds
cemonds

Reputation: 225

Scala concatenate for loop results

I'm trying to concatenate 3 sequences as results of individual for loops with yield. I can't get it to work without temporary variables. Does anybody know a better option? The notWorking version gives me a compiler error at the fourth line of the method "illegal start of a simple expression" just after the first ++.

def working() : Seq[Seq[Elem]] = {
    val result = for(index <- 0 until COMPLETE_INPUT_CHANNELS) yield {
        getModesOfCompleteInputChannel(index)
    }
    val result2 = for(index <- 0 until INCOMPLETE_INPUT_CHANNELS) yield {
        getModesOfIncompleteInputChannel(index)
    }
    val result3 = for(index <- 0 until OUTPUT_CHANNELS) yield {
        getModesOfOutputChannel(index)
    }
    return result ++ result2 ++ result3
}

def notWorking() : Seq[Seq[Elem]] = {
    for(index <- 0 until COMPLETE_INPUT_CHANNELS) yield {
        getModesOfCompleteInputChannel(index)
    } ++ for(index <- 0 until INCOMPLETE_INPUT_CHANNELS) yield {
        getModesOfIncompleteInputChannel(index)
    } ++ for(index <- 0 until OUTPUT_CHANNELS) yield {
        getModesOfOutputChannel(index)
    }

Upvotes: 3

Views: 2095

Answers (3)

Marius Danila
Marius Danila

Reputation: 10431

How about this solution ?

val tasks = Seq(
    (COMPLETE_INPUT_CHANNELS, getModesOfOutputChannel),
    (INCOMPLETE_INPUT_CHANNELS, getModesOfIncompleteInputChannel),
    (OUTPUT_CHANNELS, getModesOfOutputChannel))

tasks flatMap {
    case (limit, processing) => 0 until limit map processing
}

Upvotes: 15

Dominic Bou-Samra
Dominic Bou-Samra

Reputation: 15414

Why not this?

(0 until COMPLETE_INPUT_CHANNELS).map(getModesOfCompleteInputChannel) ++
(0 until COMPLETE_INPUT_CHANNELS).map(getModesOfIncompleteInputChannel) ++
(0 until OUTPUT_CHANNELS).map(getModesOfOutputChannel)

Though I do like M.A.D's solution. Very elegant.

Upvotes: 6

George
George

Reputation: 8378

I believe, ++ here is treated as a part of the yield expression. To make it work, just wrap your for comprehensions in parentheses.

Upvotes: 2

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