The probem is that in the case of model 2 the standard error terms reduce to a vector of length one. Since subsetting with '[' drops unneeded dimensions by default, this vector loses it's name. The solution is to add 'drop = FALSE' to your subset call, like this
ldply(fits, function(x) as.data.frame(t(coef(summary(x))[,'Std. Error', drop=FALSE]))) Best, Ista On Mon, May 17, 2010 at 5:20 AM, cfriedl <cfrieda...@gmail.com> wrote: > > I've examining a number of linear regression models on a large dataset > following the basic ideas presented here > http://www.r-bloggers.com/r-calculating-all-possible-linear-regression-models-for-a-given-set-of-predictors/ > Calculating all possible linear regressions . I run into a problem with > ldply when I have a formula that includes no intercept. Here's a simple test > to show what happens. > > # data and two linear model regressions > xy <- data.frame(cbind(x=(0:10),y=2*x + 0.2*rnorm(11))) > models <- as.list(c('y ~ x', 'y ~ -1 + x')) > models <- lapply(models, function(x) (as.formula(x)) ) > fits <- lapply(models, function(x) lm(x, data=xy)) > > # regression summaries specified individually (OK) > coef(summary(fits[[1]])) > > # Estimate Std. Error t value Pr(>|t|) > # (Intercept) -0.0594176 0.10507394 -0.5654837 5.855640e-01 > # x 2.0163534 0.01776074 113.5286997 1.620614e-15 > > coef(summary(fits[[2]])) > > # Estimate Std. Error t value Pr(>|t|) > # x 2.007865 0.00916494 219.0811 9.652427e-20 > > > # Coefficients as a dataframe using ldply (OK) > ldply(fits, function(x) as.data.frame(t(coef(x)))) > > # (Intercept) x > # 1 -0.0594176 2.016353 > # 2 NA 2.007865 > > > > # Std Errors as a dataframe using ldply (FAIL) > # variable name 'x' is missed in the second model which has no intercept. > Default variable > # name V1 is added to the output instead. > # The same behaviour is observed for 't value' and 'Pr(>|t|)' > ldply(fits, function(x) as.data.frame(t(coef(summary(x))[,'Std. Error']))) > > # (Intercept) x V1 > # 1 0.1050739 0.01776074 NA > # 2 NA NA 0.00916494 > > > Is this a bug or (hopefully) user error? Any ideas for a workaround? > > Thanks. > > > > > > > > -- > View this message in context: > http://r.789695.n4.nabble.com/Problem-with-ldply-tp2219094p2219094.html > Sent from the R help mailing list archive at Nabble.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. > -- Ista Zahn Graduate student University of Rochester Department of Clinical and Social Psychology http://yourpsyche.org ______________________________________________ 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.
