model.matrix() with na.action=NULL?

Question

I have a formula and a data frame, and I want to extract the model.matrix(). However, I need the resulting matrix to include the NAs that were found in the orig

Answer 1

Another way is to use the model.frame function with argument na.action=na.pass as your second argument to model.matrix:

> model.matrix(ff, model.frame(~ ., dat, na.action=na.pass))
   (Intercept)          b fact2 fact3 fact4 fact5
1            1 -1.3560754     0     0     0     0
2            1  2.5476965     0     0     0     0
3            1  0.4635628    NA    NA    NA    NA
4            1 -0.2871379     1     0     0     0
5            1  2.2684958     0     1     0     0
6            1 -1.3560754     0     1     0     0
7            1  2.5476965     0     0     1     0
8            1  0.4635628     0     0     1     0
9            1 -0.2871379     0     0     0     1
10           1  2.2684958     0     0     0     1

model.frame allows you to set the appropriate action for na.action which is maintained when model.matrix is called.