What does the period mean when used with ~ (in a formula)?

Question

data(iris)
subset <- cfs(Species~., iris)
f <- as.simple.formula(subset, "Species")
print(f)

Specifically, I mean the one in "Species~.".

Now, it's awfully tough to Google how a bit of punctuation is used (for me anyway) and I couldn't anything. This code is unclear.

Duplicate? http://stats.stackexchange.com/questions/10712/what-is-the-meaning-of-the-dot-in-r — Ari B. Friedman, Aug 05 '11 at 06:46
@Roman fair 'nuff, although that CV question probably belongs on SO since it has nothing to do with stats :-) — Ari B. Friedman, Aug 05 '11 at 07:10

score 21 · Answer 1 · answered Aug 05 '11 at 03:39

21

I think you're referring to the period contained in Species~., in which case this is just the standard R formulation of referring to 'all other variables' in the data frame, rather than typing them out one by one, as in Species ~ Variable1 + Variable2 etc.

From the help files of ?formula:

There are two special interpretations of . in a formula. The usual one is in the context of a data argument of model fitting functions and means ‘all columns not otherwise in the formula’: see terms.formula. In the context of update.formula, only, it means ‘what was previously in this part of the formula’.

answered Aug 05 '11 at 03:39

joran

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@Kristoff - I wrote that and then went to look up where to read about it...answer edited now. – joran Aug 05 '11 at 03:43
@Kristoff, if you found this answer to be useful and is what you were looking for, consider accepting it as the correct answer (the little gray tick that turns green when you click on it). – Roman Luštrik Aug 05 '11 at 10:33

What does the period mean when used with ~ (in a formula)?

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