CODEWITHSUNDEEP
arraysscalaoperation
Steve Wade
Steve Wade

Reputation: 13

Scala: How to use array's operation

I am trying to do operation on array in Scala.

x is a 2d-array and y is a 1d-array. For example

val x = Array(Array(1.0,2.0,3.0),Array(4.0,5.0,6.0),Array(7.0,8.0,9.0),Array(10.0,11.0,12.0).....Array(..))
val y = Array(2.0,3.0,4.0,5.0,.....n)

Assume that x.length = y.length

I wish to get a Array[Double](3) like

Array(1.0*2.0 + 4.0*3.0 + 7.0 * 4.0 + 10.0 * 5.0 ...., 2.0*2.0 + 5.0*3.0 + 8.0*4.0 + 11.0 * 5.0 ....., 3.0*2.0 + 6.0 * 3.0 + 9.0 * 4.0 + 12.0 * 5.0....)

I don't know how to do.

I used x.map(x => (x zip y).map{case(a, b) => a * b})

Obviously wrong, what's the ideal way to do that?

Thanks

Upvotes: 1

Views: 91

Answers (1)

Tzach Zohar
Tzach Zohar

Reputation: 37822

Using transpose turns x's columns into rows, which makes this easier - each column can then be zipped with y, and then the values can be multiplied and summed:

val x = Array(Array(1.0,2.0,3.0),Array(4.0,5.0,6.0),Array(7.0,8.0,9.0),Array(10.0,11.0,12.0))
val y = Array(2.0,3.0,4.0,5.0)

val result = x.transpose.map(_.zip(y).map { case (a, b) => a*b }.sum )

print(result.mkString(",")) // prints 92.0,106.0,120.0

Upvotes: 2

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