[R] ggplot2 geom_boxplot limits

[Thierry Onkelinx]

Limits in scales set values outside the limits to NA. Hence the boxplots,
smoothers,... change. Use coord_cartesian() to "zoom in".

Op 20-jul.-2015 20:29 schreef "Jacob Wegelin" <jacobwegelin op fastmail.fm>:
>
> With base graphics, one can use the "ylim" argument to zoom in on a
boxplot.
>
> With ggplot2, using "limits" to try to zoom in on a boxplot *changes the
box*.  Since the box usually indicates the 25th and 75th percentiles of a
quantitative variable, this is puzzling.
>
> The toy code below demonstrates this. In ggplot2, "zooming in" causes the
two boxes to overlap, when they did not overlap in the full plot.  Also,
the center lines --- which usually indicate the median of the variable ---
change when one zooms in.
>
> In base graphics, "zooming in" does not cause the boxes to overlap or, as
far as I can see, the median line to move relative to the scale.
>
> What is going on here?
>
> pdf(file="toy-example.pdf")
> set.seed(1)
> toy1<-data.frame(Y=rnorm(500, mean=3), A="one")
> toy2<-data.frame(Y=rnorm(500, mean=1.6), A="two")
> toy<-rbind(toy1,toy2)
> toy$A<-factor(toy$A)
> library(ggplot2)
> mybreaks<-signif(seq(from=min(toy$Y),to=max(toy$Y),by=0.5),digits=2)
> mylimits<-c(0.61,3.7)
> print(myplot<-ggplot(toy, aes(x=A,y=Y)) +
geom_boxplot()+scale_y_continuous(breaks=mybreaks)+theme_bw())
> print(myplot+scale_y_continuous(breaks=mybreaks,limits=mylimits))
> boxplot(toy1$Y,toy2$Y)
> boxplot(toy1$Y,toy2$Y, ylim=mylimits)
> graphics.off()
>
>> sessionInfo()
>
> R version 3.2.1 (2015-06-18)
> Platform: x86_64-apple-darwin13.4.0 (64-bit)
> Running under: OS X 10.10.4 (Yosemite)
>
> locale:
> [1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8
>
> attached base packages:
> [1] stats     graphics  grDevices utils     datasets  methods   base
>
> other attached packages:
> [1] ggplot2_1.0.1
>
> loaded via a namespace (and not attached):
>  [1] MASS_7.3-40      colorspace_1.2-6 scales_0.2.5     magrittr_1.5
 plyr_1.8.3       tools_3.2.1      gtable_0.1.2     reshape2_1.4.1
>  [9] Rcpp_0.11.6      stringi_0.5-5    grid_3.2.1       stringr_1.0.0
digest_0.6.8     proto_0.3-10     munsell_0.4.2
>
>
> Jacob A. Wegelin
>
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