Scala yield IndexedSeq conversion - scala

Question

I have following code snippet:
val tiles = for {
x <- 0 to bitmap.length by tileSize
y <- 0 to bitmap(0).length by tileSize
} yield new Tile[Number](x, y, tileSize, tileSize,
data = for {tx <- x to x + tileSize - 1;
ty <- y to y + tileSize - 1
} yield (bitmap(tx)(ty)))
This can look complicated, but the idea behind is to create Tile objects for every XY position in 3-dimensional bitmap object. The 'nested' yield that is given as a data parameter into the Tile's constructor is an IndexedSeq[Number], which should be converted to an Array[Number] to match the type of the data parameter. The problem is that toArray method doesn't exist for the final yielded object:
val tiles = for {
x <- 0 to bitmap.length by tileSize
y <- 0 to bitmap(0).length by tileSize
} yield new Tile[Number](x, y, tileSize, tileSize,
data = for {tx <- x to x + tileSize - 1;
ty <- y to y + tileSize - 1
} yield (bitmap(tx)(ty).toArray))
causes an error Cannot resolve symbol toArray, even though yield (bitmap(tx)(ty).toArray)) is shown as IndexedSeq[java.lang.Number] in IntelliJIDEA and theoretically should contain a definition of toArray method.
What is happening in the last yield? How can I convert resulting collection to an Array? I know, this code may and should be rewritten in simplier and more readable manner, but now I want to know, what is going on behind the curtain.

Answer 1

You need to call toArray to the final result of all the for, not to each yield.
You may do this:
val tiles = for {
x <- 0 to bitmap.length by tileSize
y <- 0 to bitmap(0).length by tileSize
} yield new Tile[Number](x, y, tileSize, tileSize,
data = (for {tx <- x to x + tileSize - 1;
ty <- y to y + tileSize - 1
} yield bitmap(tx)(ty)).toArray
However, this syntax is not encouraged in Scala, consider this snippet instead.
val tiles = for {
x <- 0 to bitmap.length by tileSize
y <- 0 to bitmap(0).length by tileSize
data = for {
tx <- x to x + tileSize - 1
ty <- y to y + tileSize - 1
} yield bitmap(tx)(ty)
tile = new Tile[Number](x, y, tileSize, tileSize, data.toArray)
} yield tile