[R] missing values

[Iasonas Lamprianou]

Dear all,
i have spent a lot of time trying to solve this problem, but I am sure that 
there must be a simple solution. So, as a last resort, I am coming back to you 
again. I have a dataset with some (almost random) values in many variables. Lets 
say that the dataset represents the scores of students to test questions. What I 
need to do is to sum the scores for each student. However, wherever there is a 
missing (NA) value, I cannot get the total score.  How can I compute the total 
score and the average per question (a) by ignoring the missing responses, (b) by 
assuming that a missing response is a zero?
Thank you for the response


 Dr. Iasonas Lamprianou




Assistant Professor (Educational Research and Evaluation)
Department of Education Sciences
European University-Cyprus
P.O. Box 22006
1516 Nicosia
Cyprus 
Tel.: +357-22-713178
Fax: +357-22-590539




Honorary Research Fellow
Department of Education
The University of Manchester
Oxford Road, Manchester M13 9PL, UK
Tel. 0044  161 275 3485
iasonas.lamprianou at manchester.ac.uk