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Simple Fix of SketchMap's non-commutative (issue-1122) #1123

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Simple Fix of SketchMap's non-commutative (issue-1122) #1123

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6 changes: 5 additions & 1 deletion algebird-core/src/main/scala/com/twitter/algebird/SketchMap.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -18,6 +18,7 @@ package com.twitter.algebird

import algebra.CommutativeMonoid
import com.twitter.algebird.matrix.AdaptiveMatrix
import com.twitter.algebird.matrix.DenseMatrix

/**
* A Sketch Map is a generalized version of the Count-Min Sketch that is an approximation of Map[K, V] that
Expand Down Expand Up @@ -50,7 +51,10 @@ class SketchMapMonoid[K, V](val params: SketchMapParams[K])(implicit
SketchMap(AdaptiveMatrix.fill(params.depth, params.width)(monoid.zero), Nil, monoid.zero)

override def plus(left: SketchMap[K, V], right: SketchMap[K, V]): SketchMap[K, V] = {
val newValuesTable = Monoid.plus(left.valuesTable, right.valuesTable)
val newValuesTable = right.valuesTable match {
case DenseMatrix(_, _, _) => Monoid.plus(right.valuesTable, left.valuesTable)
case _ => Monoid.plus(left.valuesTable, right.valuesTable)
}
Comment on lines +54 to +57
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Suggested change
val newValuesTable = right.valuesTable match {
case DenseMatrix(_, _, _) => Monoid.plus(right.valuesTable, left.valuesTable)
case _ => Monoid.plus(left.valuesTable, right.valuesTable)
}
val newValuesTable = right.valuesTable match {
case _: DenseMatrix[V] => Monoid.plus(right.valuesTable, left.valuesTable)
case _ => Monoid.plus(left.valuesTable, right.valuesTable)
}

Also, perhaps it would make more sense to address this here

algebird/algebird-core/src/main/scala/com/twitter/algebird/matrix/AdaptiveMatrix.scala

Line 56 in 65a95ce

override def plus(a: AdaptiveMatrix[V], b: AdaptiveMatrix[V]): AdaptiveMatrix[V] =

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Also, perhaps it would make more sense to address this here

yeah, pretty much agreed.
I was afraid to touch AdaptiveMatrix due to unfamiliarity of it, but will try to see if I can fix that directly.

val newHeavyHitters = left.heavyHitterKeys.toSet ++ right.heavyHitterKeys

SketchMap(
Expand Down
34 changes: 34 additions & 0 deletions algebird-test/src/test/scala/com/twitter/algebird/SketchMapTest.scala
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Original file line number Diff line number Diff line change
@@ -1,5 +1,7 @@
package com.twitter.algebird

import com.twitter.algebird.matrix.DenseMatrix
import com.twitter.algebird.matrix.SparseColumnMatrix
import org.scalacheck.{Arbitrary, Gen}
import org.scalatest.matchers.should.Matchers
import org.scalatest.wordspec.AnyWordSpec
Expand Down Expand Up @@ -53,6 +55,38 @@ class SketchMapTest extends AnyWordSpec with Matchers {
assert(sm.totalValue == totalCount)
}

"plus should work commutatively" in {
implicit val m = Monoid.longMonoid
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I believe this is not required

val valueTableLeft =
DenseMatrix(
PARAMS.width,
PARAMS.depth,
rowsByColumns = IndexedSeq(10L) ++ (1 until PARAMS.width * PARAMS.depth).map(_ => 0L)
)
val testLeft = SketchMap[Int, Long](
valuesTable = valueTableLeft,
heavyHitterKeys = List(1),
totalValue = 10
)

val valueTableRight = SparseColumnMatrix(rowsByColumns =
IndexedSeq(
SparseVector(
map = Map(1 -> 1L),
sparseValue = 1L,
length = PARAMS.width * PARAMS.depth
)
)
)
val testRight = SketchMap[Int, Long](
valuesTable = valueTableRight,
heavyHitterKeys = List(1),
totalValue = 1
)

assert(MONOID.plus(testLeft, testRight) == MONOID.plus(testRight, testLeft))
}

"exactly compute frequencies in a small stream" in {
val one = MONOID.create((1, 1L))
val two = MONOID.create((2, 1L))
Expand Down