Question

I have a Map<DateTime,Integer> rawCount, which contains raw count per date (a time-series).

I want to construct an aggregate map which will contains count during a specific interval.

For instance, if duration = (1000*1*60*60) and start = new DateTime() this map will contains total count per hour from now to the last date in the rawCount map.

I am using JodaTime, as Interval is not Comparable and I want the Map to be ordered from the most recent to the oldest date, using a TreeMap is not possible.

I am confused on which Object will be the best for my use case (is Interval appropriate?) and how to write this function.

Answer 1

This is how I would solve it.

Map<DateTime,Integer> rawCount = ....
DateTime start = ....
long duration = 1*60*60*1000;

DateTime lastDate = start;
// find the last date
for (DateTime dateTime : rawCount.keySet()) {
    if (dateTime.isAfter(lastDate))
        lastDate = dateTime;
}
int intervals = (int) ((lastDate.getMillis() - start.getMillis())/duration) + 1;
int[] counts = new int[intervals];
for (Map.Entry<DateTime, Integer> entry : rawCount.entrySet()) {
    DateTime key = entry.getKey();
    int interval = (int) ((key.getMillis() - start.getMillis()) / duration);
    counts[interval] += entry.getValue(); 
}