I need something like `fun getPartRanges(partSize: Long, totalSize: Long): List<LongRange>` th...

# getting-started

[dave08]

I need something like fun getPartRanges(partSize: Long, totalSize: Long): List<LongRange> that returns something like [0..20,21..40,41..60,61..74] for an input of partSize = 20 and totalSize = 74, what is an ideomatic way to do this in Kotlin?

[Ricky]

There's maybe no idiomatic ways to do that, but you can implement it simply yourself.

[Ricky]

Idk what you wanna do in your code, but functions chunked or windowed may help.

[dave08]

That's what I was wondering?

[karelpeeters]

(0 until totalSize).chunked(partSize)

[karelpeeters]

(if totalSize and partSize are actual sizes contrary to your example, otherwise it's .. instead of until.

[Ricky]

@karelpeeters The range will be iterated totally, and it can be avoided in a better implementation.

[karelpeeters]

Put a toSequence in there if you want.

[dave08]

Just about to say that, the Long is a file size and the range is the current range of the file that needs to be downloaded...

[dave08]

So it could be 60mb in a bytes Long and iterate to get a list of all the numbers in between instead of just returning from where to start and where to end the current download @karelpeeters...

[dave08]

But I thought there might at least be a few things in stdlib that could help... maybe reduce?

[karelpeeters]

(0 .. totalSize/partSize).map { it .. min((1 + it) * partSize, totalSize }

[Ricky]

A little long, you can try this if you don't mind.

fun getPartRanges(partSize: Long, totalSize: Long): List<LongRange> {
    val fullPartCount = (totalSize / partSize).toInt()
    val perfect = totalSize % partSize == 0L
    val partRanges = ArrayList<LongRange>(fullPartCount + if (perfect) 0 else 1)

    var current = 0L
    var next = partSize
    while (next < totalSize) {
        partRanges += current until next
        current = next
        next += partSize
    }

    if (!perfect) partRanges += current until totalSize

    return partRanges
}

[karelpeeters]

Idiomatic

Writes the most procedural code possible 😉

[dave08]

Thanks, I'll give those a try simple smile .....

[dave08]

@karelpeeters Looks like (0L .. totalSize/partSize).map { (it * partSize) .. min((it * partSize) + partSize + 1, totalSize) } works! Thanks a lot! And thanks for the try @Ricky, if anything it just goes to show how Kotlin goes a long way 🙂 !