I'm trying to write a function, using `dplyr` syntax, which includes grouping with group\_by inside the function. There seems to be a problem with the `group_by` statement, and I can't figure out whats wrong. When I pass `abc` as an argument and using `select` inside the function, it works as i would have expected (Gfunc1). When trying to `group_by` the same argument, it gives me an error; 

> 
> Error: Column `dims` is unknown 
> 
> 
> 

Please see exampel below. I really hope I have not overlooked some embarrassingly simple thing... anyway, would be gratefull for help!

```
library(dplyr)

abc <- c("a","a","a","b","b","c")
num <- c(1,2,3,4,5,6) 
df <- data.frame(abc,num)

Gfunc1 <- function(dims) {
test1 <- df %>% 
    select(dims)
assign("test1", test1, envir = .GlobalEnv)
}

Gfunc2 <- function(dims) {
test2 <- df %>% 
  group_by(dims)

assign("test2", test2, envir = .GlobalEnv)
}

Gfunc1("abc") 
# Returns as expected; df test1 with only col = "abc"

Gfunc2("abc")
# Does not return what i expect; gives error:  Error: Column `dims` is unknown 

```