Can’t copy from my computer as gmail is blocked at work but if it helps, the “predvars” attribute if the terms object is not the same.
Avi On Fri, Apr 27, 2018 at 9:25 AM Hadley Wickham <[email protected]> wrote: > Hi all, > > Very surprising (to me!) and mystifying result from predict.glm(): the > predictions vary depending on whether or not I use ns() or > splines::ns(). Reprex follows: > > library(splines) > > set.seed(12345) > dat <- data.frame(claim = rbinom(1000, 1, 0.5)) > mns <- c(3.4, 3.6) > sds <- c(0.24, 0.35) > dat$wind <- exp(rnorm(nrow(dat), mean = mns[dat$claim + 1], sd = > sds[dat$claim + 1])) > dat <- dat[order(dat$wind), ] > > m1 <- glm(claim ~ ns(wind, df = 5), data = dat, family = binomial) > m2 <- glm(claim ~ splines::ns(wind, df = 5), data = dat, family = binomial) > > # The model coefficients are the same > unname(coef(m1)) > #> [1] 0.5194712 -0.8687737 -0.6803954 4.0838947 2.3908674 4.1564128 > unname(coef(m2)) > #> [1] 0.5194712 -0.8687737 -0.6803954 4.0838947 2.3908674 4.1564128 > > # But the predictions are not! > newdf <- data.frame(wind = seq(min(dat$wind), max(dat$wind), length = 5)) > unname(predict(m1, newdata = newdf)) > #> [1] 0.51947119 0.03208719 2.82548847 3.90883496 4.06743266 > unname(predict(m2, newdata = newdf)) > #> [1] 0.5194712 -0.5666554 -0.1731268 2.8134844 3.9295814 > > Is this a bug? > > (Motivating issue from this ggplot2 bug report: > https://github.com/tidyverse/ggplot2/issues/2426) > > Thanks! > > Hadley > > > > -- > http://hadley.nz > > ______________________________________________ > [email protected] mailing list > https://stat.ethz.ch/mailman/listinfo/r-devel > -- Sent from Gmail Mobile [[alternative HTML version deleted]] ______________________________________________ [email protected] mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
