Trip Discovery - By Origin Cell, Count Trips to Common Destination Cell

TripCorrRed.reduce.java

    public void reduce(Text key, Iterable<TripCorrWrit> values, Context ctx)
        throws IOException, InterruptedException {

        final int INIT_SIZE = 8000;
        HashMap<String,Long> records = new HashMap<String,Long>(INIT_SIZE);

        String sval, maxDest = null;
        long totCount = 0, maxCount = 0;
        for (TripCorrWrit entry : values) {
            sval = entry.toString();  // bounds of destination cell - value of iterator, key of hashmap
            long newCount = records.containsKey(sval) ? 1 + records.get(sval) : 1;
            records.put(sval, newCount);
            if (newCount > maxCount) {
                maxCount = newCount;
                maxDest = sval;
            }
            totCount++;
        }  // /for
        Configuration config = ctx.getConfiguration();
        int minPoints = config.getInt("com.esri.trip.threshold", 10);  //minimum count per cell
        minPoints = minPoints < 2 ? 1 : minPoints;
        if (totCount >= minPoints) {
            double pct = 0.;
            if (maxCount > 1)  // if only one trip going to each destination cell, report zero correlation.
                pct = 100. * (double)maxCount / (double)totCount;
            ctx.write(key, new Text(String.format("%d\t%d\t%f\t%s",
                                                  totCount, maxCount, pct,  // calculated numbers
                                                  maxDest)));  // most common destination cell (bounds)
        }
    }