There are two questions about dplyr, which in my case are related to the problem I am trying to solve:

• How can I cross-classify usage data_frame
  
  with pipes when trying to pipe the resulting series of operations to xtabs
  
  ?
• The pipe argument is usually denoted .
  
  in dplyr
  
  and magrittr
  
  , but it is also the token used to denote everything else in the formula interface. I know there is some open issue in dplyr
  
  (can't find it right now) that talks about replacing .
  
  with _
  
  .

Here's an example:

wakefield::r_data_frame(
  n = 100,
  cat1 = r_sample_factor(x = LETTERS[1:3]),
  cat2 = r_sample_factor(x = LETTERS[1:3]),
  cat3 = r_sample_factor(x = LETTERS[1:3]),
  bin1 = r_sample_logical()
) %>%
  dplyr::filter(bin1) %>%
  xtabs(. ~ cat1 + cat2 + cat3, data = .)

      

        
        
        
      

    

which fails with output:

Error in model.frame.default(formula = . ~ cat1 + cat2 + cat3, data = .) : 
  invalid type (list) for variable '.' 

      

        
        
        
      

    

because it magrittr

replaces the first one .

with the result of data_frame

previous calculations. One way is to completely omit the first period, for example:

wakefield::r_data_frame(
  n = 100,
  cat1 = r_sample_factor(x = LETTERS[1:3]),
  cat2 = r_sample_factor(x = LETTERS[1:3]),
  cat3 = r_sample_factor(x = LETTERS[1:3]),
  bin1 = r_sample_logical()
) %>%
  dplyr::filter(bin1) %>%
  xtabs( ~ cat1 + cat2 + cat3, data = .)

      

        
        
        
      

    

But what if .

you had to cross to the other side formula

?

Edit:

As @MrFlick pointed out, xtabs

doesn't accept RHS anyway .

. I thought this problem could also be illustrated using the RHS conflict .

I was expecting with code:

wakefield::r_data_frame(
  n = 100,
  cat1 = r_sample_factor(x = LETTERS[1:3]),
  cat2 = r_sample_factor(x = LETTERS[1:3]),
  cat3 = r_sample_factor(x = LETTERS[1:3]),
  bin1 = r_sample_logical()
) %>%
  dplyr::filter(bin1) %>%
  dplyr::select(-bin1) %>%
  xtabs( ~ ., data = .)

      

        
        
        
      

    

but this works exactly as expected. Can someone explain why magrittr

not trying to replace the first .

with data_frame

?