If you have 60 rows and 3 columns in matrix 'a' then you can find the mean of each row i.e. the first three values as you stated above then you should use:
nanmean(a,2);
nanmean calculates the mean without considering the nan and the 2, tells matlab to calculate the mean along the second dimension i.e. for each row. stating nanmean(a,1) would calculate the mean for each individual column thus returning 60 values. Hope this helps
