Use input of a function as variable name in R - r

Question

I have a simple function in R to modify a dataframe
monthly_fun <- function(x){
x %>%
mutate(obstime = convert_dates(obstime)) %>%
select(obstime, x = obsvalue)
}
When applying the function to dataframe df, i.e. monthly_fun(df), I would like df to be the name of obsvalue. In my current code, the name is obviously "x", how can I modify the part in select to get the name of the supplied dataframe as the variable name instead?
Thanks a lot
EDIT: I want to apply this function to several dataframes using
result <- list( df1, df2, df3) %>%
lapply( monthly_fun )

Answer 1

You could extract the name of input by deparse(substitute(x)), and use !!y := obsvalue in mutate().
monthly_fun <- function(x) {
y <- deparse(substitute(x))
x %>%
mutate(obstime = convert_dates(obstime),
!!y := obsvalue) %>%
select(obstime, y)
}
A simplified example:
fun <- function(x) {
y <- deparse(substitute(x))
x %>%
mutate(!!y := 1) %>%
select(y)
}
fun(df)
# df
# 1 1
# 2 1
# 3 1
# 4 1
# 5 1
Update
If you want to apply it to several data frames stored in a list, you should design a 2-argument function, one argument for data and the other for new column names. Then use Map() to apply this function over each pair of data and names.
fun <- function(x, y) {
x %>%
mutate(!!y := 1) %>%
select(y)
}
Map(fun, list(df1, df2), c("name1", "name2"))
# [[1]]
# name1
# 1 1
# 2 1
# 3 1
# 4 1
# 5 1
#
# [[2]]
# name2
# 1 1
# 2 1
# 3 1
# 4 1
# 5 1
If you're familiar with purrr, The use of Map can be replaced with map2() or imap(). (Notice the difference of inputs to the both functions)
library(purrr)
# (1) map2(): Input data and names separately
map2(list(df1, df2), c("name1", "name2"), fun)
# (2) imap(): Input a named list
imap(list(name1 = df1, name2 = df2), fun)

Answer 2

Using the suggestion by Julien and creating a variable using deparse(substitute(df)) and rename using that.
monthly_fun <- function(x) {
y = deparse(substitute(x))
x <- x %>%
mutate(obstime = obstime*5) %>%
select(obstime, obsvalue)
names(x)[names(x) == "obsvalue"] <- y
return(x)
}
see this site for more naming methods.