Handling missing combinations of factors in R

Question

So, I have a data frame with two factors and one numeric variable like so:

>D
f1 f2 v1 
1   A  23
2   A  45
2   B  27
     .
     .
     .

Answer 1

I add the tidyr solution, spreading with fill=0 and gathering.

library(tidyr)
df %>% spread(f2, v1, fill=0) %>% gather(f2, v1, -f1)

#  f1 f2 v1
#1  1  A 23
#2  2  A 45
#3  1  B  0
#4  2  B 27

You could equally do df %>% spread(f1, v1, fill=0) %>% gather(f1, v1, -f2).