code: public SingleOutputStreamOperator<T> minBy(String field, boolean first) {
  		return aggregate(new ComparableAggregator<>(field, input.getType(), AggregationFunction.AggregationType.MINBY, first, input.getExecutionConfig()));
  	}
docs: Applies an aggregation that that gives the minimum element of the pojo
  data stream by the given field expression for every window. A field
  expression is either the name of a public field or a getter method with
  parentheses of the {@link DataStream DataStreams} underlying type. A dot can be used
  to drill down into objects, as in {@code "field1.getInnerField2()" }.
  
  @param field The field expression based on which the aggregation will be applied.
  @param first If True then in case of field equality the first object will be returned
  @return The transformed DataStream.