code: public void minimumExistingDatapoints(Map<Long, Double> datapoints) {
  		if (datapoints != null) {
  
  			for(Entry<Long, Double> entry : datapoints.entrySet()){
  				Double existingValue = _datapoints.get(entry.getKey());
  				if(existingValue == null){
  					_datapoints.put(entry.getKey(), entry.getValue());
  				} else if (existingValue > entry.getValue()) {
  					_datapoints.put(entry.getKey(), entry.getValue());
  				}
  			}
  		}
  	}
docs: If current set already has a value at that timestamp then sets the minimum of the two values for that timestamp at coinciding cutoff boundary,
  else adds the new data points to the current set.
  
  @param  datapoints  The set of data points to add. If null or empty, no operation is performed.