r - How to complete missing factor levels in data frame?

Question

Lets pretend I have something like this:

df <- data.frame(
      PERSON = c("Peter", "Peter", "Marcel" , "Lisa", "Lisa"),        
      FRUIT = c("Apple", "Peach","Apple", "Apple", "Peach" ), 
      A = c(100, 200, 100, 200, 300), 
      B=c(1,2,3,4,5) )
df$PERSON <- as.factor(df$Person)
df$FRUIT <- factor(df$FRUIT, levels = c("Apple", "Peach", "Coconut"))

Which resulsts in

str(df): 'data.frame':  5 obs. of  4 variables:
$ PERSON: Factor w/ 3 levels "Lisa","Marcel",..: 3 3 2 1 1
$ FRUIT : Factor w/ 3 levels "Apple","Peach",..: 1 2 1 1 2
$ A     : num  100 200 100 200 300
$ B     : num  1 2 3 4 5

I want to expand this data, frame so that for every PERSON there are all levels of FRUIT present, like this:

 Person FRUIT   A B
1  Peter Apple 100 1
2  Peter Peach 200 2
3  Peter Coconut 0 0
4 Marcel Apple 100 3
5 Marcel Peach 0 0
6 Marcel Coconut 0 0
7   Lisa Apple 200 4
8   Lisa Peach 300 5
9   Lisa Coconut 0 0

Missing values for A and B should be filled with 0.

I tried tidyr::complete(df$FRUIT, 0), but it seems, that I used this function wrong.

Answer 1

The complete takes the first argument as 'data', followed by the columns to expand. By default, the fill is NA, but we can change it to 0 by specifying it in a list.

complete(df, PERSON, FRUIT, fill = list(A=0, B = 0))