Use column index instead of name in group_by

Question

I want to summarize a dataframe with dplyr, like so:

> test <-data.frame(ID = c(\"A\", \"A\", \"B\", \"B\"), val = c(1:4))
> test %>% group_by(ID         


        

Answer 1

If we need to use NSE, then sym and !! can be used

test %>%
     group_by(!! rlang::sym(names(.)[1])) %>%
     summarise(av = mean(val))
# A tibble: 2 x 2
#      ID    av
#   
#1      A   1.5
#2      B   3.5

We can also create a function. If we pass quoted strings, then we use sym with !! or else go for the enquo/!! route

f1 <- function(dat, grp, valueCol) {
     dat %>%
        group_by(!! rlang::sym(grp)) %>%
        summarise(av = mean(!! rlang::sym(valueCol)))
}

f1(test, "ID", "val")
# A tibble: 2 x 2
#      ID    av
#   
#1      A   1.5
#2      B   3.5