tabyl handles grouped data.frame inputs

closes #125

R/tabyl.R

@@ -119,7 +119,8 @@ tabyl.default <- function(dat, show_na = TRUE, ...) {
 tabyl.data.frame <- function(dat, var1, var2, var3, show_na = TRUE, ...){
   if("data.frame" %in% class(dat) &
      missing(var1) & missing(var2) & missing(var3)){stop("if calling on a data.frame, specify unquoted column names(s) to tabulate.  Did you mean to call tabyl() on a vector?")}
-  # TODO: check that variable names are present in data.frame
+  if(dplyr::is_grouped_df(dat)){ dat <- dplyr::ungroup(dat) } 
+
   if(missing(var2) & missing(var3)){
     tabyl_1way(dat, rlang::enquo(var1), show_na = show_na)
   } else if(missing(var3)){

tests/testthat/test-tabyl.R

@@ -123,7 +123,13 @@ test_that("bizarre combination of %>%, quotes, and spaces in names is handled",
   )
 })
 
+test_that("grouped data.frame inputs are handled (#125)", {
+  expect_equal(mtcars %>% group_by(cyl) %>% tabyl(carb, gear),
+               mtcars %>% tabyl(carb, gear))
+})
+
 test_that("if called on non-existent vector, returns useful error message", {
   expect_error(tabyl(mtcars$moose), "object mtcars\\$moose not found")
   expect_error(tabyl(moose), "object 'moose' not found")
+  expect_error(mtcars %>% tabyl(moose), "object 'moose' not found")
 })