Vasco - 8 months ago 59

Scala Question

I am getting inconsistent answers from the following code which I find odd.

`import scala.math.pow`

val p = 2

val a = Array(1,2,3)

println(a.par

.aggregate("0")((x, y) => s"$y pow $p; ", (x, y) => x + y))

for (i <- 1 to 100) {

println(a.par

.aggregate(0.0)((x, y) => pow(y, p), (x, y) => x + y) == 14)

}

a.map(x => pow(x,p)).sum

In the code the

`a.par ...`

`14`

`10`

Answer

In your "seqop" function, that is the first function you pass to `aggregate`

, you define the logic that is used to combine elements within the *same* partition. Your function looks like this:

```
(x, y) => pow(y, p)
```

The problem is that you don't accumulate the results of a partition. Instead, you throw away your accumulator `x`

. Every time you get 10 as a result, the calculation `2^2`

was dropped.

If you change your function to take the accumulated value into account, you will get 14 every time:

```
(x, y) => x + pow(y, p)
```

Source (Stackoverflow)