(R) IF statement: stop & warn if FALSE else continue

Question

I'm making a function and before it does any of the hard stuff I need it to check that all the column names listed in the 'samples' dataset are also present in the 'grids' dataset (the function maps one onto the other).

all(names(samples[expvar]) %in% names(grids))

This does that: the code within all() asks if all the names in the list ('expvar') of columns in 'samples' are also names in 'grids'. The output for a correct length=3, expvar would be TRUE TRUE TRUE. 'all' asks if all are TRUE, so the output here is TRUE. I want to make an IF statement along the lines of:

if(all(names(samples[expvar]) %in% names(grids)) = FALSE) {stop("Not all expvar column names found as column names in grids")}

No else needed, it'll just carry on. The problem is that the '= FALSE' is redundant because all() is a logically evaluable statement... is there a "carry on" function, e.g.

if(all(etc)) CARRYON else {stop("warning")}

Or, can anyone think of a way I can restructure this to make it work?

Answer 1

You're looking for the function stopifnot.

However you don't need to implement it as

if (okay) {
  # do stuff
} else {
  stop()
}

which is what you have. Instead you can do

if (!okay) {
  stop()
}
# do stuff

since the lines will execute in sequential order. But, again, it might be more readable to use stopifnot, as in:

stopifnot(okay)
# do stuff