Scala Array Slicing with Tuple

Question

I try to slice an 1D Array[Double] using the slice method. I've written a method which returns the start and end index as a tuple (Int,Int).

  def getSliceRange(): (Int,Int) = {
    val start =   ...
    val end =  ...
    return (start,end)
  }

How can I use the return value of getSliceRange directly?

I tried:

myArray.slice.tupled(getSliceRange())

But this gives my a compile-Error:

Error:(162, 13) missing arguments for method slice in trait IndexedSeqOptimized;
follow this method with `_' if you want to treat it as a partially applied function
  myArray.slice.tupled(getSliceRange())

Peter Neyens · Accepted Answer · 2016-06-29 12:55:02Z

5

I think the problem is the implicit conversion from Array to ArrayOps (which gets slice from GenTraversableLike).

val doubleArray = Array(1d, 2, 3, 4)

(doubleArray.slice(_, _)).tupled

Function.tupled[Int, Int, Array[Double]](doubleArray.slice)

(doubleArray.slice: (Int, Int) => Array[Double]).tupled

answered Jun 29, 2016 at 12:55

Peter Neyens

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3 Comments

Tzach Zohar Over a year ago

in short: (myArray.slice(_, _)).tupled(getSliceRange()) does the trick.

Raphael Roth Over a year ago

Can you explain what (doubleArray.slice(_, _)).tupled means?

Peter Neyens Over a year ago

doubleArray.slice(_, _) is the same as (a, b) => doubleArray.slice(a, b), we need the parentheses because we want to call tupled on the function and not on the result of slice .

meucaa · Accepted Answer · 2016-06-29 12:59:52Z

1

Two options here, the first one is to call your function twice:

myArray.slice(getSliceRange()._1, getSliceRange()._2)

or to save your Tuple beforehand:

val myTuple: (Int, Int) = getSliceRange()
myArray.slice(myTuple._1, myTuple._2)

Edit: I leave this here just in case but Peter Neyens posted the expected answer.

edited Jun 29, 2016 at 12:59

answered Jun 29, 2016 at 12:48

meucaa

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