Guava's Immutable filtering via Java 8 parallel stream : Need help in filtering Guava's ImmutableTable via parallel stream and collector

    Immutable<fieldA1,fieldB1,Boolean> validEntry;
    Immutable<ObjectA, String, ObjectB> tofilter;

    ObjectA{
    String fieldA1
    String fieldA2
    }
    ObjectB{
    String fieldB1
    String fieldB2
    }

Usecase : iterate over toFilter and remove elements which are not present or entry value is false in validEntry table.

     Map<ObjectA, Map<String, ObjectB>> rowMap = toFIlter.rowMap();
     //This will result into stream of stream
     for(loop over rowMap){

     for(Loop over rowMap entry){
      if(present in validEntry){
        //add entry to new table
       }
     }
    }

build new table

How can i utilize flat map to convert this stream of streams.
