Is there a Scala way of selecting a subset of List[Array[Int]] by checking each element of each Arra-CodePudding

New to Scala. I have data of the form List[Array[Int]],each Array[Int] has n integers, call this a. There are also two Array[int], call them c and d, also of length n. I want to compare each element of each row of a to the corresponding element of c and d (i.e, of same index) and return those rows that match c or d.

Nothing at stake here, just self teaching Scala.

CodePudding user response：

Examples are better than explanations (don't describe, demonstrate) so it's a little hard to know if this is what you're getting at.

val data = List(Array( 2, 4, 6)  // a
               ,Array(11,44, 6)  // c
               ,Array(12, 4,66)) // d

data.transpose
    .flatMap(grp => grp.tail.find(_ == grp.head))
//res0: List[Int] = List(4, 6)

This is a bit dangerous in that all the arrays must be non-empty and the same length.

CodePudding user response：

Assuming this starting point:

val c = Array(1,2,3)
val d = Array(0,1,2)
val target: List[Array[Int]] = List(c,d)

val as: List[Array[Int]] =
  List(
    Array(0,1,2),
    Array(1,2,3),
    Array(2,3,4),
    Array(4,5,6),
  )

Here is how to get only the arrays from as that match exactly c or d:

as
  .filter(a => a.sameElements(c) || a.sameElements(d))


//and a bit more generic if you have a big target pool
as
  .filter(a => target.exists(_.sameElements(a)))

This solution is resilient to possible empty or different sizes arrays in as.