Hi Ivo, See inline.
On Fri, Jul 8, 2011 at 3:42 PM, ivo welch <ivowe...@gmail.com> wrote: > dear R wizards---more ignorance on my part, exacerbated by too few > examples in the function documentations. > >> d <- data.frame( id=rep(1:3,3), x=rnorm(9), y=rnorm(9)) > > Question 1: how do I work with the output of "by"? for example, > >> b <- by( d, d$id, function(x) coef(lm( y ~ x, data=x ) )) >> b > > d$id: 1 > (Intercept) x > 0.2303 0.3618 > --------------------------------------------------------------------------------------------------- > d$id: 2 > (Intercept) x > 0.05785 -0.40617 > --------------------------------------------------------------------------------------------------- > d$id: 3 > (Intercept) x > 0.269 -0.378 > > getting the categories is easy: > >> names(b) > [1] "1" "2" "3" > > but how do I transform the non-name info in this by() data structure > into a matrix with dimensions 3 by 2? (presumably, there is some > vector operator that can do this kind of magic.) Here is one option: a <- do.call(cbind, b) > > > Question 2: Let's say I want to add only one of the two coefficients > to d. The naive approach > a <- ave( d, d$id, FUN=function(x) coef(lm( y ~ x, data=x ))[2] ) > gives me the right coefficient in each row, but overwrites every > entry. I guess I can keep only the first column of a, and add it to > d, but this seems a rather ugly and inefficient way. How is this done > better? Do you actually want the coefficients duplicated for every row where id is the same? d$coef <- a[, as.character(d$id)] > > Question 3: repeat question 2, but keep both the intercept and the slope. d <- cbind(d, t(a[, as.character(d$id)])) though you'll get a rowname warning HTH, Josh > > > thanks in advance, as always, for any advice. > > /iaw > ---- > Ivo Welch (ivo.we...@gmail.com) > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > -- Joshua Wiley Ph.D. Student, Health Psychology University of California, Los Angeles https://joshuawiley.com/ ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
