From: Dirk Eddelbuettel <edd_at_debian.org>

Date: Wed, 17 Mar 2010 20:41:54 -0500

Date: Wed, 17 Mar 2010 20:41:54 -0500

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_at_r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-develReceived on Thu 18 Mar 2010 - 01:43:46 GMT

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