Proper idiom for adding zero count rows in tidyr/dplyr

Question

Suppose I have some count data that looks like this:

library(tidyr)
library(dplyr)

X.raw <- data.frame(
    x = as.factor(c(\"A\", \"A\", \"A\", \"B\", \         


        

Answer 1

You can use tidyr's expand to make all combinations of levels of factors, and then left_join:

X.tidy %>% expand(x, y) %>% left_join(X.tidy)

# Joining by: c("x", "y")
# Source: local data frame [4 x 3]
# 
#   x  y count
# 1 A  i     1
# 2 A ii     5
# 3 B  i    15
# 4 B ii    NA

Then you may keep values as NAs or replace them with 0 or any other value. That way isn't a complete solution of the problem too, but it's faster and more RAM-friendly than spread & gather.