apache spark - scala type mismatch error in graphX code -

i'm new scala, learning apache-spark. wrote simple function in scala graphx

def foo(edge: edgetriplet[map[long, double], double]): iterator[(vertexid, map[long, double])] = {      val m = edge.srcattr      for((k, v) <- m){         if (v + edge.attr < edge.dstattr.getorelse(k, 10.0))             iterator(edge.dstid, map(k -> v + edge.attr))          else              iterator.empty      }  } 

errors

name: compile error message: <console>:37: error: type mismatch;  found   : double  required: string                    iterator(edge.dstid, map(k -> v + edge.attr))                                                           ^ <console>:35: error: type mismatch;  found   : unit  required: iterator[(org.apache.spark.graphx.vertexid, map[long,double])]     (which expands to)  iterator[(long, map[long,double])]            for((k, v) <- m){                       ^ stacktrace: 

why scala treating v string? , cause of second error?

after editing code suggested @alexey, i'm getting error

name: compile error message: <console>:30: error: type mismatch;  found   : scala.collection.immutable.map[org.apache.spark.graphx.vertexid,scala.collection.immutable.map[long,double]]     (which expands to)  scala.collection.immutable.map[long,scala.collection.immutable.map[long,double]]  required: iterator[(org.apache.spark.graphx.vertexid, map[long,double])]     (which expands to)  iterator[(long, map[long,double])]                  (k, v) <- edge.srcattr                         ^ stacktrace: 

if helps, i'm implementing different version of sendmessage function code

the first common problem + in scala, unfortunately. in case have not k -> (v + edge.attr), expected, (k -> v) + edge.attr. , + method on tuple2 accepts string. fix it, add correct parentheses.

the second error because for(...) { ... } returns unit (it's translated foreach call). missing yield. in fact if want use for, should like

for {   (k, v) <- m   x <- if (v + edge.attr < edge.dstattr.getorelse(k, 10.0))       iterator((edge.dstid, map(k -> (v + edge.attr))))     else       iterator.empty[(long, map[long,double])] } yield x 

i'd prefer write as

m.flatmap { case (k, v) =>    if (v + edge.attr < edge.dstattr.getorelse(k, 10.0))     iterator((edge.dstid, map(k -> (v + edge.attr))))   else     iterator.empty[(long, map[long,double])] }