@Override public ToDoubleFunction<Stream<Tuple2<F,Double>>> dist(Stream<Tuple2<F,Double>> features1){
  Object2DoubleMap<F> auxMap=new Object2DoubleOpenHashMap<>();
  auxMap.defaultReturnValue(0.0);
  DoubleAdder norm1=new DoubleAdder();
  features1.forEach(null);
  if (norm1.doubleValue() == 0) {
    return null;
  }
  return null;
}

@ Override public ToDoubleFunction < Stream < Tuple2 < F , Double > > > dist ( Stream < Tuple2 < F , Double > > features1 ) { Object2DoubleMap < F > auxMap = new Object2DoubleOpenHashMap < > ( ) ; auxMap . defaultReturnValue ( 0.0 ) ; DoubleAdder norm1 = new DoubleAdder ( ) ; features1 . forEach ( null ) ; if ( norm1 . doubleValue ( ) == 0 ) { return null ; } return null ; }
returns a function that returns the feature - based similarity to the features of an item .
