How MapReduce Works
- We will understand MapReduce with the help of an example
- Word count example
- Imagine a huge data set that contains user comments and discussions about a laptop
- We want to count the frequency of words to get an idea on the popular features
Map Reduce Word Count Example
The Map Function input and output
- Input
- Map function takes a key and value pair as input
- Key = Text document name
- Value = the contents of text document
- Output
- Map function gives key value pairs as output
- Key = word
- Value = 1
Map Reduce Word Count Example
How Map Function Works
The Reduce Function input and output
- Input
- Reduce function takes a key and set of value pair as input
- Key=word
- Value=all counts list of that word
- Output
- Reduce function gives key value pairs as output
- Key=word
- Value=sum of counts
How Reduce Function Works
