# select(group_by(.)) implicitely adds grouping variables (#170) Code res <- mtcars %>% group_by(vs) %>% select(mpg) Message Adding missing grouping variables: `vs` # group_by works with zero-row data frames (#486) Code x <- select(dfg, a) Message Adding missing grouping variables: `g` # group_by() and ungroup() give meaningful error messages Code df <- tibble(x = 1, y = 2) (expect_error(df %>% group_by(unknown))) Output <error/rlang_error> Error in `group_by()`: ! Must group by variables found in `.data`. x Column `unknown` is not found. Code (expect_error(df %>% ungroup(x))) Output <error/rlib_error_dots_nonempty> Error in `ungroup()`: ! `...` must be empty. x Problematic argument: * ..1 = x i Did you forget to name an argument? Code (expect_error(df %>% group_by(x, y) %>% ungroup(z))) Output <error/vctrs_error_subscript_oob> Error in `ungroup()`: ! Can't subset columns that don't exist. x Column `z` doesn't exist. Code (expect_error(df %>% group_by(z = a + 1))) Output <error/rlang_error> Error in `group_by()`: ! Problem adding computed columns. Caused by error in `mutate()`: ! Problem while computing `z = a + 1`. Caused by error in `mask$eval_all_mutate()`: ! object 'a' not found
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