R function with list of variables of unknown length - r

Question

trying to branch out an learn some R, one thing I do often at my job is I pull weighted means by some time specific period variable. I figured out how to do that individually like this:
means_by_period <- df %>%
group_by(period) %>%
summarize(var1 = weighted.mean(var1, wgtvar),
var2 = weighted.mean(var2, wgtvar),
var3 = weighted.mean(var3, wgtvar),
var4 = weighted.mean(var4, wgtvar)
)
We do this all the time but I am not always going to know how many variables/what variables I am going to be pulling and it would be a pain to edit this code every time, so I built an excel sheet to do it for me, but this seems like a good opportunity to learn how to write a function to do it. Problem is I am not sure how to write it such that it will work. I know my arguments will be: 1. the current data set 2. the period 3. the weighted variable 4. a concatenated vector of my variables?
newfunction <- function(df, period, weight, variables)
{df %>%
group_by(period) %>%
summarize(var1 = weighted.mean(var1, weight),
var2 = weighted.mean(var2, weight),
var3 = weighted.mean(var3, weight),
var4 = weighted.mean(var4, weight) )
}
I am like 2 weeks into learning so if anyone could give me some pointers on what I'd need to do here that would be great. Thanks!

Answer 1

If the 'var1', 'var2', 'var3', 'var4' are a vector of column names (as strings in the 'variables', then we can convert to symbol and evaluate (!!)
library(dplyr)
newfunction <- function(df, period, weight, variables) {
df %>%
group_by({{period}}) %>%
summarize(
!! variables[1] := weighted.mean( !! rlang::sym(variables[1]), {{weight}}),
!! variables[2] := weighted.mean( !! rlang::sym(variables[2]), {{weight}}),
!! variables[3] := weighted.mean( !! rlang::sym(variables[3]), {{weight}}),
!! variables[4] := weighted.mean( !! rlang::sym(variables[4]), {{weight}}) )
}
Here, the column names for 'period', 'weight' are assumed to be passed as unquoted, while the 'variables' as a vector of strings
As the OP mentioned that 'variables' can be of unknown length, we can loop over the vector of column names ('variables') in map
library(purrr)
newfunction2 <- function(df, period, weight, variables) {
map(variables, ~ df %>%
group_by({{period}}) %>%
summarise(!! .x := weighted.mean(!! rlang::sym(.x), {{weight}}))) %>%
reduce(full_join)
}