[MapReduce] 그림으로 이해하는 하둡 맵리듀스 예제

word counting example 

1) first, text file should be converted to key-value type 

2) map function can map each word to value one 

3) same key will be grouped and passed to reducer. then reduce function can just sum values over same key

 

 

how selection works

 

how projection works