On 6/14/05, Ajay Narottam Shah <[EMAIL PROTECTED]> wrote: > > > I have a program which is doing a few thousand runs of lm(). Suppose > > > it is a simple model > > > y = a + bx1 + cx2 + e > > > > > > I have the R object "d" where > > > d <- summary(lm(y ~ x1 + x2)) > > > > > > I would like to obtain Var(x2) out of "d". How might I do it? > > > > > > I can, of course, always do sd(x2). But it would be much more > > > convenient if I could snoop around the contents of summary.lm and > > > extract Var() out of it. I couldn't readily see how. Would you know > > > what would click? > > > > Is the question how to get the variance of a column of the > > model matrix for a model that is the sum of terms given only > > summary output and the column name but not the name of the > > data frame? If that is it then try this: > > > > d <- summary(lm(Sepal.Length ~ Sepal.Width, iris)) # test data > > var(model.matrix(eval(d$call))[,"Sepal.Width"]) > > Yes, this is indeed exactly what I was looking for :-) Thanks, > > The eval() pays the full cost of running d$call?
Yes. It reruns it. If we can assume that the second arg to lm is data= then we could do this which simply grabs the indicated column from the data frame: f <- function(d, name) eval(substitute(with(eval(d$call[[3]]), name))) f(d, Sepal.Width) # same as iris$Sepal.Width # or f <- function(d, charname) eval(d$call[[3]])[[charname]] f(d, "Sepal.Width") ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html