How to use group_by() with an empty argument, in R? - r

Question

I am writing a function that computes the mean of a variable according to some grouping (g1 and g2). I would like the function to take care of the case when the user just wants to compute the mean across the groups, so the group argument will be empty.
I want a solution using tidyverse.
Suppose the following:
y = 1:4
g1 = c('a', 'a', 'b', 'b')
g2 = c(1,2,1,2)
MyData = data.frame(g1, g2, y)
MyFun = function(group){
group_sym = syms(group)
MyData %>%
group_by(!!!group_sym) %>%
summarise(mean = mean(y))
}
# this works well
MyFun(group = c('g1', 'g2'))
Now suppose I want the mean of y across all groups. I would like the function be able to treat something like
MyFun(group = '')
or
MyFun(group = NULL)
So ideally I would like the group argument to be empty / null and thus MyData would not be grouped. One solution could be to add a condition at the beginning of the function checking if the argument is empty and if TRUE write summarise without group_by. But this is not elegant and my real code is much longer than just a few lines.
Any idea?

Answer 1

1) Use {{...}} and use g1 in place of 'g1':
MyFun = function(group) {
MyData %>%
group_by({{group}}) %>%
summarise(mean = mean(y)) %>%
ungroup
}
MyFun(g1)
## # A tibble: 2 x 2
## g1 mean
## <fct> <dbl>
## 1 a 1.5
## 2 b 3.5
MyFun()
## # A tibble: 1 x 1
## mean
## <dbl>
## 1 2.5
2) This approach uses 'g1' as in the question.
MyFun = function(group) {
group <- if (missing(group)) 'All' else sym(group)
MyData %>%
group_by(!!group) %>%
summarise(mean = mean(y)) %>%
ungroup
}
MyFun('g1')
## # A tibble: 2 x 2
## g1 mean
## <fct> <dbl>
## 1 a 1.5
## 2 b 3.5
MyFun()
## # A tibble: 1 x 2
## `"All"` mean
## <chr> <dbl>
## 1 All 2.5
3) This also works and gives the same output as (2).
MyFun = function(...) {
group <- if (...length()) syms(...) else 'All'
MyData %>%
group_by(!!!group) %>%
summarise(mean = mean(y)) %>%
ungroup
}
MyFun('g1')
MyFun()

Answer 2

A different approach consists of creating a fake group (named 'across_group') in the data, in the case of group is missing.
MyFun = function(group) {
if (missing(group)) MyData$across_group = 1
group <- if (missing(group)) syms('across_group') else syms(group)
MyData %>%
group_by(!!!group) %>%
summarise(mean = mean(y)) %>%
ungroup
}
MyFun()
# A tibble: 1 x 2
across_group mean
<dbl> <dbl>
1 1 2.5