output NULL of key and val

[nguyenvanlinh1808]

hi everybody,
I succeeded run Hadoop jar,
yarn jar $YARN_EXAMPLES/hadoop-mapreduce-examples-3.1.0.jar pi 2 4
It gives the results. That means the mapreduce job is successful.

However, when I run it in R
from.dfs(mapreduce(input = to.dfs(1:10), map = function(k,v) keyval(v, v^2)))
It always returns NULL of key and val. The other wordcount mapreduce also brings me a NULL value of val and key.

Please help me to find out a solution for such issue.
Thank you very much!