Using rollmean when there are missing values (NA)

Use 'partial=TRUE' option. The option makes it possible to calculate data with NA.

> rollapply(z, width=3, FUN=function(x) mean(x, na.rm=TRUE), by=1, by.column=TRUE, partial=TRUE, fill=NA, align="right")

     a    b        c
1  0.0  NaN 1.000000
2  0.5 10.0 5.500000
3  1.0  9.5 4.333333
4  2.0  9.0 6.666667
5  3.0  8.0 4.666667
6  4.0  7.0 6.000000
7  5.0  6.0 7.000000
8  6.0  5.0 8.666667
9  7.0  4.0 8.333333
10 8.0  3.0 7.000000
11 9.0  2.0 5.000000

If you want to change 'NaN' in the first row to '0', modify 'fill=NA' to 'fill=0'.

From ?rollmean

The default method of ‘rollmean’ does not handle inputs that contain ‘NA’s. In such cases, use ‘rollapply’ instead.