When writing R functions always remind yourself to think about if it can happen that you accidentally just select one column of a
This will result in vector which might not be what you expect in the following code.
One good practice is to always use
drop=FALSE when you intend to get a
data.frame and use the
[] notation if you expect a vector.
Lets assume cols is a vector which only sometimes has the length one, then we would do the following:
And to purposefully select a vector: