Mappers and Reducers

Here's a quick but comprehensive introduction to the idea of splitting tasks into a MapReduce model.
The four important functions involved are:

Map (the mapper function)  
EmitIntermediate(the intermediate key,value pairs emitted by the mapper functions)  
Reduce (the reducer function)  
Emit (the final output, after summarization from the Reduce functions)

We provide you with a single system, single thread version of a basic MapReduce implementation.

Task

The given input has a number of rows, each with four fields from a table, containing:

Country, State, City, Population of the city    

You are required to output:

Country, State, Population of the state (obtained by summing up the population of each city in that state)  

The code for the MapReduce class, reading and splitting the text, parts related to IO etc. has already been provided. However certain parts of the mapper and reducer functions are incomplete. You need to replace the questionmarks (?). Your task is to fill up these question marks appropriately, such that the program works, and outputs the number of times each word occurs.
Also, this program outputs certain information to the error stream. This information has been logged to help beginners gain a better understanding of the the intermediate steps in a map-reduce process.

Language Support
Java, Python and Ruby.