rcomp | Simple output testing for command line applications | Unit Testing library

The signs of eigenvectors and loadings are arbitrary, so there is nothing "wrong" here. The only thing that you should expect to be preserved is the overall pattern of signs within each loadings vector, i.e. in the example above the princomp answer for PC1 gives +,+,-,-,- while yours gives -,-,+,+,+. That's fine. If yours gave e.g. -,+,-,-,+ that would be trouble (because the two would no longer be equivalent up to multiplication by -1).

However, while it's generally true that the signs are arbitrary and hence could vary across algorithms, compilers, operating systems, etc., there's an easy solution in this particular case. princomp has a fix_sign argument:

fix_sign: Should the signs of the loadings and scores be chosen so that the first element of each loading is non-negative?

Try princomp(df,fix_sign=FALSE)$scores and you'll see that the signs (probably!) line up with your results. (In general the fix_sign=TRUE option is useful because it breaks the symmetry in a specific way and thus will always result in the same answers across all platforms.)