Am I the only one who thinks this is bad explanation?
"Supriya : But how I will create different types of Chutneys?
Shekhar : Now you will see the missing phase of MapReduce — Shuffle phase. MapReduce will group all the outputs written by every Map based on the key. This will be automatically done for you. You can assume key as just a name of ingredient like Onion. So all the onion keys will be grouped together and will be transferred to a grinder which will just process onions. So, you will get onion Chutney. Similarly all the tomatoes will be transferred to the grinder marked for tomato and will produce tomato Chutney."
On a side note, I was surprised when MapReduce made such waves, as it's nothing _new_, per se. I still can't believe Google was granted a patent for it. I wrote "MapReduce"-esque algorithms in early high school when I made a distributed system to compute Pi. All it really does is provide a framework for creating, dispatching and joining jobs.