Alex Rivera | Logout

Listing combinations WITH repetitions in Scala

Asked 2009-07-01T19:20:23.453
10

Trying to learn a bit of Scala and ran into this problem. I found a solution for all combinations without repetions here and I somewhat understand the idea behind it but some of the syntax is messing me up. I also don't think the solution is appropriate for a case WITH repetitions. I was wondering if anyone could suggest a bit of code that I could work from. I have plenty of material on combinatorics and understand the problem and iterative solutions to it, I am just looking for the scala-y way of doing it.

Thanks

scala combinatorics
Edit
Report

1 Answer

7

Meanwhile, combinations have become integral part of the scala collections: 

scala> val li = List (1, 1, 0, 0) 
li: List[Int] = List(1, 1, 0, 0)

scala> li.combinations (2) .toList
res210: List[List[Int]] = List(List(1, 1), List(1, 0), List(0, 0))

As we see, it doesn't allow repetition, but to allow them is simple with combinations though: Enumerate every element of your collection (0 to li.size-1) and map to element in the list:

scala> (0 to li.length-1).combinations (2).toList .map (v=>(li(v(0)), li(v(1))))
res214: List[(Int, Int)] = List((1,1), (1,0), (1,0), (1,0), (1,0), (0,0))
answered 2012-06-18T06:15:39.293

Your Answer