(Scalding) groupBy foldLeft using the group by value in the fold

Question

Have data like :

pid  recom-pid
1   1
1   2
1   3
2   1
2   2
2   4
2   5

Need to make it :

pid, recommendations
1    2,3
2    1,4,5

Meaning ignore self from the 2nd column, and make the rest in to a comma separated string. Its tab separated data

Tried variations of, but not sure how to refer to productId in the foldLeft

.groupBy('productId) {     
  _.foldLeft(('prodReco) -> 'prodsR)("") {
    (s: String, s2: String) =>
      {
        println(" s " + s + ", s2 :" + s2 + "; pid :" + productId + ".")
        if (productId.equals(s2)) {
          s
        } else {
          s + "," + s2;
        }
      }
  }
}

Using scala 2.10 with scalding 0.10.0 and cascading 2.5.3. Need a scalding answer. I know how to manipulate the data in scala. I'm just wondering how to get hold of the columns during group by in scalding and use them to conditionally do a fold left or other means to get the filtered output.

For a full working sample see https://github.com/tgkprog/scaldingEx2/tree/master/Q1

Answer 1

Instead of groupBy and then foldLeft, use just foldLeft.
Here is a solution using scala collections but it should works using scalading as well:

val source = List((1,1), (1,2), (1,3), (2,1), (2,2), (2,4), (2,5))                                                                                
source.foldLeft(Map[Int, List[Int]]())((m,e) =>                                
  if (e._1 == e._2) m else m + (e._1 -> (e._2 :: m.getOrElse(e._1, List()))))  

Answer 2

Just a groupBy and a map should be enough to accomplish what you want.

// Input data formatted as a list of tuples.
val tt = Seq((1, 1), (1, 2), (1, 3), (2, 1), (2, 2), (2, 4), (2, 5))

tt
  .groupBy(_._1) // Map(2 -> List((2, 1), ...), 1 -> List((1, 1), ...))
  .toSeq // for easier mapping
  .map({
    case (pid, recomPids) => {
      val pids = recomPids.collect({
        case recomPid if recomPid._2 != pid => recomPid._2
      })
      (pid, pids)
     }
   }) // List((2, List(1, 4, 5)), (1, List(2, 3)))

I simplified the input/output form to just focus on getting the collections into the right form.

Answer 3

Assume pid| recom-pid > temp.txt and so

import scala.io.Source
val xs = Source.fromFile("temp.txt").getLines.toArray.map(_.split("\\|"))

We convert xs into tuples, like this

val pairs = for (Array(pid, recom) <- xs) yield (pid,recom)
Array((1,1), (1,2), (1,3), (2,1), (2,2), (2,4), (2,5))

and group by the first element,

val g = pairs.groupBy(_._1)
Map(2 -> Array((2,1), (2,2), (2,4), (2,5)), 1 -> Array((1,1), (1,2), (1,3)))

Then we remove mapped identity tuples, which ensures always an entry in the map, where an empty array denotes there was only the identity tuple (viz. unique occurrence of 3|3 would lead to 3 -> Array()),

val res = g.mapValues(_.filter { case (a,b) => a != b } )
Map(2 -> Array((2,1), (2,4), (2,5)), 1 -> Array((1,2), (1,3)))

Answer 4

Asssuming your string input is correct that returns you a Map[String, Array[String]]

s.split('\n')
.map(_.split("\\|"))
.groupBy(_(0))
.mapValues(_.flatten)
.transform {case (k, v) ⇒ v.filter(_ != k)}