hadoop - Can We generate 2 pairs of (key, value) in one map function? If yes how? -

i have dataset of userid , post related each userid. want count number of posts each user. want put posts of each userid (concat posts separation).

any suggestions how go it?

imho, can have mapper , reducer.

mapper:

1. class postmapper extends mapper < object, text, text, text>
2. map() can write key userid (text) , value post(text) context.

reducer:

1. class postreducer extends reducer < text, text, text, text >

2. reduce() can have iterable loop (i) counter counts every fetched post , (ii) text variable can used concatenate every fetched post suitable delimiter.

3. after completing loop, key / userid and, value / the
   concatenated text can written reducer's context.

after job ran successfully, resulting file contain userid , concatenated posts, separated tab.

note: remove tab characters in posts before concatenate. prefix count followed tab , append concatenated posts if want count in output.