@risdenk Yes, running Custom MapReduce jobs in Hortonworks Sandbox is interesting.  In fact, I wanted to try out an experiment of running a custom MapReduce job in Sandbox and I succeeded after many failed attempts.

The failures were mainly due to the way users and groups are configured in Sandbox.

Anyways, since I succeeded, here I am, writing a tutorial for the same on Community Tutorials section.

Thanks and Regards,
Vivek Ganesan