public void reduce(LongWritable key, Iterable<Text> values, Context context)
throws IOException, InterruptedException {
LongWritable curNodeId = key;
double previousPRValue = 1;
double nextPRValue = 0;
double localResidual = 0;
String edgeListOfCurNode = "";
long localResidualTransformed = 0;
for (Text value : values) {
String[] inputInfo = value.toString().split("\\s+");
// incoming pagerank value
if (inputInfo.length == 1) {
nextPRValue += Double.parseDouble(inputInfo[0]);
}
// current node info
else if (inputInfo.length == 3) {
edgeListOfCurNode = inputInfo[2];
previousPRValue = Double.parseDouble(inputInfo[1]);
} else if (inputInfo.length == 2) {
previousPRValue = Double.parseDouble(inputInfo[1]);
} else {
System.out.println("ERROR: received unexpected TEXT in length");
}
}
if (previousPRValue == 1) System.out.println("No node info has been received by a reducer");
// calculate the pagerank value according to the given formula
nextPRValue = pagerankFormula(nextPRValue);
// should also iterate sink nodes list, add the evenly splitted value
// reducer should store the updated node info(NPR) to output directory
context.write(null, new Text(curNodeId + " " + nextPRValue + " " + edgeListOfCurNode));
// then compare PPR with NPR
try {
localResidual = Math.abs(previousPRValue - nextPRValue) / nextPRValue;
localResidualTransformed = (long) (localResidual * 10000);
// System.out.println("Make sure you got the right transformed residual :
// "+localResidualTransformed);
} catch (ArithmeticException e) {
System.out.println("PPR is zero. Check where you get the value!");
}
// assume there is a global counter called residualCounter;
context.getCounter(myCounter.ResidualCounter.RESIDUAL_SUM).increment(localResidualTransformed);
}
