[R] formula
Adaikalavan Ramasamy
ramasamy at cancer.org.uk
Thu Jul 15 18:04:56 CEST 2004
If you want to fit "y = a + bx", then you use "lm(y ~ x)" instead of "lm(y ~ A + bx)".
See the details section of help("formula").
> x <- 1:5
> y <- c(0, 1.0, 1.7, 2.0, 2.1)
> lm(x ~ y)
Call:
lm(formula = x ~ y)
Coefficients:
(Intercept) y
0.6828 1.7038
If A was already defined, and you are trying to multiply the y-values, then use the I() operator.
This protects the term/calculation and inhibits the usual term interpretation in linear models.
> lm(x ~ I(2*y) )
Call:
lm(formula = x ~ I(2 * y))
Coefficients:
(Intercept) I(2 * y)
0.6828 0.8519
PS : I think there is a typo in the y input as there is no such number as 2.1.4
On Thu, 2004-07-15 at 16:28, solares at unsl.edu.ar wrote:
> Hi, i 'dont understand how to take a general formula, view this:
>
> x<-1:5
> y<-c(0,1,1.7,2,2.1.4)
> dummy<-data.frame(x=x,y=y)
> formula<-"y~A*log(x)/log(2)"
> formu<-as.formula(formula)
> fm<-lm(formu,data=dummy)
> Error in eval(expr, envir, enclos) : Object "A" not found
>
> but A is the parameter of fitting, why is this?Thanks Ruben
>
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