Question about sum of Map[String, Map[String, Int]]

[Liren Sun]

Hi, 

I have a problem when I try to sum Map[String, Map[String, Int]].

When the first operant is a key point to a empty map, it was not being calculate into the result.

 

scala> val d1 = Map("a"->Map[String, Int]())

d1: scala.collection.immutable.Map[String,scala.collection.immutable.Map[String,Int]] = Map(a -> Map())

scala> val d2 = Map("b"->Map[String,Int]())

d2: scala.collection.immutable.Map[String,scala.collection.immutable.Map[String,Int]] = Map(b -> Map())

scala> val d3=d1+d2

d3: scala.collection.immutable.Map[String,scala.collection.immutable.Map[String,Int]] = Map(b -> Map())

// I was expecting Map[String,Int]] = Map(a->Map(), b -> Map())

scala> val d1 = Map("a"->Map[String, Int]("a"->1))

d1: scala.collection.immutable.Map[String,scala.collection.immutable.Map[String,Int]] = Map(a -> Map(a -> 1))

scala> val d3=d1+d2

d3: scala.collection.immutable.Map[String,scala.collection.immutable.Map[String,Int]] = Map(b -> Map(), a -> Map(a -> 1))

// Same as what I expected

scala> val d1 = Map("a"->Map[String, Int]())

d1: scala.collection.immutable.Map[String,scala.collection.immutable.Map[String,Int]] = Map(a -> Map())

scala> val d2 = Map("b"->Map[String,Int]("a"->1))

d2: scala.collection.immutable.Map[String,scala.collection.immutable.Map[String,Int]] = Map(b -> Map(a -> 1))

scala> val d3=d1+d2

d3: scala.collection.immutable.Map[String,scala.collection.immutable.Map[String,Int]] = Map(b -> Map(a -> 1))

// I was expecting Map(a->Map(), b->Map(a->1))

Thanks

[Liren Sun]

scala> val y = implicitly[Monoid[Map[String, Map[String, Int]]]]

y: com.twitter.algebird.Monoid[Map[String,Map[String,Int]]] = com.twitter.algebird.MapMonoid@50bfd130

scala> y.isNonZero(d1)

res12: Boolean = false

scala> d1

res13: scala.collection.immutable.Map[String,scala.collection.immutable.Map[String,Int]] = Map(a -> Map())