Hadoop MapReduce - Join of two files and Computation on grouped values

Question

I am fairly new to Hadoop and MapReduce programming. I want to know whether it is possible to group by another value (not key) after joining of two files.

I have two files which have following data

File1

name    marks
A       Male
B       Male
C       Female

File2

name    marks
A       25
B       28
A       30
C       22

Now is there any method to find the percentage of marks for each gender. I am trying to get the following as output

Male    percentage_of_marks_of_male_students
Female  percentage_of_marks_of_female_students

Is there anyway to do this in a single job. I've tried using two jobs for this, but couldn't find any headway.

Any tips would be appreciated.