On 17 March 2010 at 16:32, Ross Boylan wrote: | While browsing some code I discovered a call to lm that used a formula y | ~ X - 1, where X was a matrix. | | Looking through the documentation of formula, lm, model.matrix and maybe | some others I couldn't find this useage (R 2.10.1). Is it anything I | can count on in future versions? Is there documentation I've | overlooked?
>From help(formula): Details: In addition to ‘+’ and ‘:’, a number of other operators are useful in model formulae. [...] The ‘-’ operator removes the specified terms, so that ‘(a+b+c)^2 - a:b’ is identical to ‘a + b + c + b:c + a:c’. It can also used to remove the intercept term: ‘y ~ x - 1’ is a line through the origin. A model with no intercept can be also specified as ‘y ~ x + 0’ or ‘y ~ 0 + x’. What exactly are you questioning? That X is a matrix? That doesn't take away from the fact that the rest is a formula. Dirk -- Registration is open for the 2nd International conference R / Finance 2010 See http://www.RinFinance.com for details, and see you in Chicago in April! ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel