davidandrzej

function [l v] = grasshopper(W, r, lambda, k)
%
% Reranking items by random walk on graph with absorbing states.
% (CREDIT: Jerry Zhu jerryzhu@cs.wisc.edu)
%  
% INPUT 
% 
%   W: n*n weight matrix with non-negative entries.
%      W(i,j) = edge weight for the edge i->j
%      The graph can be directed or undirected.  Self-edges are allowed.

davidandrzej

Keybase proof

I hereby claim:

• I am davidandrzej on github.
• I am davidandrzej (https://keybase.io/davidandrzej) on keybase.
• I have a public key whose fingerprint is 5203 3009 B157 505D DF21 9C16 B86B BB05 D29E 1BFE

To claim this, I am signing this object:

davidandrzej

scala> implicit val em = EvaluationMonoid
em: EvaluationMonoid.type = EvaluationMonoid$@34f5b235

scala> implicit val mm = mapMonoid[String,Evaluation]
mm: scalaz.Monoid[Map[String,Evaluation]] = scalaz.std.MapInstances$$anon$4@13105b09

scala> val dataset1 = Map("modelA" -> Evaluation(3,2),
|                          "modelB" -> Evaluation(4,1))
dataset1: scala.collection.immutable.Map[String,Evaluation] = 
    Map(modelA -> Evaluation(3,2), modelB -> Evaluation(4,1))

davidandrzej

val evalGen = for {total <- Gen.choose(0, 1000);
                  correct <- Gen.choose(0, total)} 
                      yield Evaluation(total,correct)

"Evaluation Monoid" should {

    import EvaluationMonoid._
    implicit val eq = Equal.equalA[Evaluation]
 
    "obey Monoid typeclass Law" in {

davidandrzej

"Evaluation Monoid" should {

    import EvaluationMonoid._
    implicit val eq = Equal.equalA[Evaluation]
    val testEvaluation = Evaluation(3, 2)

    "obey Monoid typeclass Law" in {
        Monoid.monoidLaw.leftIdentity(testEval) should be (true)
        Monoid.monoidLaw.rightIdentity(testEval) should be (true)
    }

davidandrzej

object EvaluationMonoid extends Monoid[Evaluation] {
     def zero = Evaluation(0,0)
     def append(x: Evaluation, y: => Evaluation) =
         Evaluation(x.total + y.total, x.correct + y.correct)
}

davidandrzej

case class Evaluation(total: Int, correct: Int)

davidandrzej

trait Monoid[F] extends Semigroup[F] { 
    ...
    trait MonoidLaw extends SemigroupLaw {
        def leftIdentity(a: F)(implicit F: Equal[F]) = 
            F.equal(a, append(zero, a))
        def rightIdentity(a: F)(implicit F: Equal[F]) = 
            F.equal(a, append(a, zero))
    }
    ...
}

davidandrzej

def addItUp[F : Monoid](items: Seq[F]): F = {
    // Combine a bunch of items
    val m = implicitly[Monoid[F]]
    items.foldLeft(m.zero){case (total, next) => m.append(total,next)}
}

scala> addItUp(Seq("day ", "after ", "day"))
res1: String = "day after day"
scala> addItUp(Seq(1,2,3))
res2: Int = 6

davidandrzej

trait Monoid[F] {
  def zero: F
  def append(f1: F, f2: => F): F
}