Writing/applying "subtract the mean"-function to standardize regression parameters - r

Question

I was trying to write and apply a seemingly easy function that would standardize my continuous regression parameters/ predictors. The reason is that I want to deal with multicollinearity.
So instead of writing x-mean(x,na.rm=T) each time, I'm looking for something more handy which does the job for me - not least because I wanted to exercize writing functions in R. ;)
So here is what I tried:
fun <- function(data.frame, x){
data.frame$x - mean(data.frame$x, na.rm=T)
}
Apparently this is not too wrong. At least it doesn't return an error message.
However, applying fun to, say, the built-in mtcars dataset and, say, the variable disp yields this error message:
#Loading the data:
data("mtcars")
fun(mtcars,x=disp) #I tried several ways, e.g. w and w/o "mtcars" in front
Warning message:
In mean.default(mtcars$x, na.rm = T) :
argument is not numeric or logical: returning NA
My guess is that it is about how I applied the function, because when I do manually what the function is supposed to do, it works perfectly.
Also, I was looking for similar questions on writing and applying such a function (also beyond the Stack Exchange universe), but I didn't find anything helpful.
Hope I didn't make a blunder due to my novice R-skills.

Answer 1

There is already a function in R which does what you want to do: scale().
You can just write scale(mtcars$hp, center = TRUE, scale = FALSE) which then subtracts the mean of the vector from the vector itself.
In combination with apply this is powerful; You can, for example center every column of your dataframe by writing:
apply(dataframe, MARGIN = 2, FUN = scale, center = TRUE, scale = FALSE)
Before you do that you have to make sure that this is a valid function for your column. You cannot scale factors or characters, for example.
In regards to your question: Your function should have to look like this:
fun <- function(data.frame, x){
data.frame[[x]] - mean(data.frame[[x]], na.rm=T)
}
and then when specifying the function you would have to write fun(mtcars, "hp") and specify the variable name in quotation marks. This is because of the special way the $ operator works, you cannot use a character string after it.