Map-reduce code for finding average salary

Question

I have a file with below details
emp_id,salary
a,1000
b,3000

If I want to write a map-reduce code for finding average salary among all the employees, What will my key-value pair for mapper and reducer as input and output?

Answer 1

You can choose your mapper output key to be a string such as 

Mapper <key,value> = "average salary ",1000

                                     "average salary ",3000

Reducer input <key,value> =  "average salary ",(1000,3000)

Reducer output <key,value> = "average salary ",4000