What is the difference between . and .data?

Question

I\'m trying to develop a deeper understanding of using the dot (".") with dplyr and using the .data pronoun with dplyr. The code

Answer 1

Compare mtcars %>% count(.data[["cyl"]]) vs. mtcars %>% count(.[["cyl"]]).

mtcars %>% count(.[["cyl"]])
  .[["cyl"]]  n
1          4 11
2          6  7
3          8 14


mtcars %>% count(.data[["cyl"]])
  cyl  n
1   4 11
2   6  7
3   8 14

. is literally just the previous result. So the first is similar to:

. <- mtcars
count(., .[["cyl"]])

The second is a shorthand for looking up the variable by the string "cyl" and treating the previous result as the search path for the variable. For example, suppose you mispelled your variable name:

mtcars %>% count(.[["cyll"]])
   n
1 32

mtcars %>% count(.data[["cyll"]])
Error: Must group by variables found in `.data`.
* Column `cyll` is not found.

Using . will not throw an error because indexing to a non-existing column is a valid base-R operation that returns NULL.

Using .data will throw because using a non-existent variable:

mtcars %>% count(cyll)

Also throws.