RandomProjection.scala

//See http://en.wikipedia.org/wiki/Locality-sensitive_hashing#Random_projection

class RandomProjection(dimensions : Int, nBuckets : Int, bitsPerBucket : Int) {
  val seed = 123456789
  lazy val r = new scala.util.Random(seed)
  lazy val buckets =
    (1 to nBuckets).map{i =>
      (1 to bitsPerBucket).map{j =>
        (1 to dimensions).map{k =>
          val f = r.nextDouble
          if(r.nextBoolean)
            f
          else
            f * -1
        }
      }
    }

  def apply(s : Seq[Double]) : Seq[Int] = {
    buckets.map{bucket =>
      bucket.zipWithIndex.map{
        case (plane, i) =>
        val dotProd = (plane,s).zipped.map{_*_}.sum
        if(dotProd > 0)
          2 << i
        else
          0
      }.sum
    }
  }
}

class RandomProjection2(nBuckets : Int, bitsPerBucket : Int)
  extends RandomProjection(2, nBuckets, bitsPerBucket) {

  def apply(v1 : Double, v2 : Double) : Seq[Int] = apply(List(v1, v2))
}

class RandomProjection3(nBuckets : Int, bitsPerBucket : Int)
  extends RandomProjection(3, nBuckets, bitsPerBucket) {

  def apply(v1 : Double, v2 : Double, v3 : Double) : Seq[Int] = apply(List(v1, v2, v3))
}