Averaging and then using grpstats in Matlab?

I have NDVI reading for 5 times in same spot, I first want to use means of 5 values and then using grpstats as function to get the mean value on the basis of Date, Pasture, and Patches. I use NDVImean = grpstats([date Pasture Patches NDVI],[date,Pasture,Patches],'nanmean'); but since the data, Pasture and Patches are 495*1 while NDVI is 2351*1. Could anyone help me please?

[Image Analyst]

If you take the mean of 5 in the 2351 NVDI vector, you'll have 2351/5 = 470.2. How exactly are those means supposed to match up with the 495 elements in the other vectors? The lengths don't match.

[Sonisa]

Yes, that is true. But it should have 2475 data file, some were missing so it came around 2351. We collect the data on same day and time since some of the data were not good we have to eradicate it. so is there anyway that I can make the elements of both vector working for each other?