How can I build a function in R that will take a numerical variable as a column name?

I am trying to create a function that will use a number it is passed as a column name for a dataframe. This sounds sort of silly because normally I wouldn’t use numbers as column names, but in this case I’m actually trying to work with a BchronCalibratedDates object produced by the Bchron package, and it is a nested list named after the sample ID, which is usually a number.

Anyway, a simple reproducible example of what I’m trying to do would be something like:

a <- 1:5
dat <- tibble("1" = a, "2" = a*2)

test <- function(x) {
dat$"x"
}

Where I could then call test(1) and get an output of [1] 1 2 3 4 5.

When I run this code now, it returns NULL with a warning message "Unknown or uninitialized column: ‘x’." How can I fix this?

>Solution :

You can use [[

test <- function(x) {
    dat[[as.character(x)]]
}

or get

test <- function(x) {
    get(as.symbol(x), dat)
}

such that

> test(1)
[1] 1 2 3 4 5