Getting a range of data from infinite time series

Question

I have a map storing the time series data in following format

HashMap<Date,Double> infiniteTimeSeries;

The variable infiniteTimeSeries can have data from 1AD to even 2100AD. When the user asks the values between Jan-1-1970 to Jan-1-1972, I need to pick the data corresponding to only the requested time range.

Is there an easy way to do this? Like a library. I am trying to avoid looping on the map , as the map can even have 100 years of data and iterating like 300000 elements for a short requested time range will affect the performance badly

Kindly please provide your valuable suggestions

Answer 1

You could use a TreeMap instead of a HashMap.

A TreeMap is sorted, by default, by the natural ordering of its keys. The java.util.Date class defines a natural ordering by implementing Comparable<Date>.

From the TreeMap, you can get a subset of the map over a range of keys, using TreeMap.subMap(). This version extends from fromKey inclusive to toKey exclusive. (A sibling allows other options.)

public SortedMap<K,V> subMap(K fromKey,
                         K toKey)

By the way, if you're working in Java 8, you might consider using the new Instant class instead of the older Date class. Instant also implements Comparable.