How to sort data in map reduce hadoop?

Question

I am working with a programme that has 4 MapReduce steps.the output of my first step is:

id      value
 1        20
 2         3
 3         9
 4        36


        

Answer 1

If you want to sort according to value's, make it key in map function. i.e.

id      value
1        20
2         3
3         9
4        36
5         3

(value) (key) in map function

output will be 

key      value
3         5
3         2
9         3
20        1
36        4

map<value, id> output key/value  
reduce <value, id>

if you want id to be in the first column, this will work.

context.write(value, key);

Note that, id's are not going to be sorted