How to embed if statement inside a map

I have a definition calculation cosine similarity for each combination coming from a matrix. However, I want the definition runs under some certain conditions.

The definition is given below:

def neighbours(signatures: Iterable[Signature], minCosineSimilarity: Double): Iterator[MatrixEntry] = {
   signatures.
      toSeq.
      sortBy(_.index). // sort in order to create an upper triangular matrix
      combinations(2)
      .map {
        case first :: other :: nil =>
        if((first.index < 4 && other.index > 3) || (first.index > 3 && other.index < 4)){}
        val cosine = Cosine(first.vector, other.vector)
        MatrixEntry(first.index, other.index, cosine)
    }.
      filter(_.value >= minCosineSimilarity)
  }

It calculates cosine similarity for a given pair coming from "combinations(2)" line. I have added a line containing if statement. How can I make this if condition valid here?