[Rd] y ~ X 1 , X a matrix
Dirk Eddelbuettel
edd at debian.org
Thu Mar 18 02:41:54 CET 2010
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

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