mongodb - Error on return a Future[Boolean] from a for in Scala -

I am writing the application 2.3.2 in Scala.

I use reactive Mongo as a driver. My mongodab database I have a collection called "recommendation.tagsSimilarity", which has the value of similarity between my tags, where a tag is in the form Is: "category: attribute".

An example of a document is as follows:

  {"_id": ObjectId ("5440ec6e4165e71ac4b53a71"), "id": "10912199495810912197116116114-10912199581091219711611611450", "tags 1 ":" 10912199495810912197116116114 "," tag1Name ":" myc1: Myattr "," tag2 ":" 10912199581091219711611611450 "," tag2name ":" myc: myattr2 "," eq ": 0}  

A domain represents an element of the matrix of nxn dimensions, where n is the number of saved tags.

Now I have created a collection called "recommendation.correlation", on which I save the connection between "category" and a tag.

To do this, I am writing a method that repeats elements of tag simulation as matrix. Future [Boolean] = {def calculation (category: string, tag: hard g): future [(double, double)] = {// correlation calculation and tupal values Back) play.Logger.debug ("Start Correlation") similarity. all. Twistlistat {tag match = & gt; Get tag category for (i & lt; - tag match) {val category = i.tag1Name.split (":") (0) // (j Category, "Attribute" -> ProductName) Correlation. Query, correlation, upset = true) flatMap {status = & gt; Situation match {case final end (fine, _, _, _, _, _, _) = & gt; Future {true} case _ = & gt; Future (false)}}}}}}

but the compiler gives me the following error:

  [error] / user / alberto / git / Bdrim / modules / recommendation-system / app / recommendationsystem / algorithms / Pearson.scala313: type mismatch; [Error] found: unit [error] is required: scala.concurrent.future [boolean] for [error] (i & lt; - tag match) {[error] ^ [error] / user / alberto / git / bdri / Module / recommendation - system / app / referral system / algorithm / pearson Scala: 313: Type Mismatch; [Error] found: unit [error] required: scala.concurrent.future [boolean] [error] for (i & lt; - tag match) {[error] ^ [error] got an error  

What's wrong ?? I do not understand why do not return anything for the statement. In addition to this I would like to ask why I can not write the code to iterate twice in the list in Scala.

you to yield with for Forgot to use:

For the (i & lt; - tag match) {. ..} is translated into a foreach instruction

(i <- tag match) yield {...} By using this it will actually translate into map / flatmap and generate results (this is for both of its code s).