CODEWITHSUNDEEP
scalafunctional-programming
Gaurav Abbi
Gaurav Abbi

Reputation: 645

finding a position of an element in a list of lists in functional programming

I am looking for an elegant solution for finding the position of an element in a seq of sequences. e.g.

def findChar(c: Char, levelVector: Vector[Vector[Char]]): (x,y) = {
     val x = levelVector.indexWhere(vect=>vect.indexOf(c) != -1)
    (x,levelVector(x).indexOf(c))
}

this works fine, but somehow I have a gut feeling, there should be a better elegant solution , some scala or FP construct which i am not able to recall [long years of imperative programming can do this kind of damage :) ]. which lets me do the work of

vect.indexOf(c)

only once. I have explored other constructs like flattening or for comprehension, but does not seems elegant or simple. we can assume that vector is non-empty and element is unique.

any suggestions appreciated.

Upvotes: 2

Views: 157

Answers (2)

vijucat
vijucat

Reputation: 2088

Neither elegant nor succinct, but a solution nevertheless, one that I hammered out because I forced myself to do it using a for comprehension:

  def findChar(c: Char, levelVector: Vector[Vector[Char]]): (Int, Int) = {
    val y = for (
      i <- 0 to levelVector.view.length - 1;
      v = levelVector.view(i);

      j = v.indexOf(c) if j != -1
    ) yield (i, j)

    y.take(1)(0)
  }

I might delete this answer soon :-)

Upvotes: 0

Alexey Romanov
Alexey Romanov

Reputation: 170745

Something like this should work

def findChar(c: Char, levelVector: Vector[Vector[Char]]) = {
  // view is to ensure indices are only calculated up to the element you need
  val vec1 = levelVector.view.map(_.indexOf(c))
  val x = vec1.indexWhere(_ != -1)
  if (x != -1)
    Some((x, vec1(x)))
  else
    None // or (-1, -1) if you prefer
}

Upvotes: 2

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