Factors in R: more than an annoyance?

Question

One of the basic data types in R is factors. In my experience factors are basically a pain and I never use them. I always convert to characters. I feel oddly like I\'m missi

Answer 1

A factor is most analogous to an enumerated type in other languages. Its appropriate use is for a variable which can only take on one of prescribed set of values. In these cases, not every possible allowed value may be present in any particular set of data and the "empty" levels accurately reflect that.

Consider some examples. For some data which was collected all across the United States, the state should be recorded as a factor. In this case, the fact that no cases were collected from a particular state is relevant. There could have been data from that state, but there happened (for whatever reason, which may be a reason of interest) to not be. If hometown was collected, it would not be a factor. There is not a pre-stated set of possible hometowns. If data were collected from three towns rather than nationally, the town would be a factor: there are three choices that were given at the outset and if no relevant cases/data were found in one of those three towns, that is relevant.

Other aspects of factors, such as providing a way to give an arbitrary sort order to a set of strings, are useful secondary characteristics of factors, but are not the reason for their existence.