[R] ggplot2 argument handling odd

[hadley wickham]

On Wed, Mar 26, 2008 at 11:03 AM, Sebastian Weber
<sebastian.weber at physik.tu-darmstadt.de> wrote:
> Hello there,
>
>  I'm trying to do lots of plots in one for-loop. But somehow ggplot does
>  not evaluate arguments as expected. Here is an example:
>
>  library(lattice)
>  library(ggplot2)
>  pl <- list()
>  pl2 <- list()
>  cDat <- as.data.frame(cbind(x1=0:100,x2=0:10,x3=1:20))
>  for(obs in c("x1", "x2")) {
>   pl[[obs]] <- xyplot(cDat[,obs] ~ cDat[,"x3"], main=obs)
>   pl2[[obs]] <- qplot(cDat[,"x3"], cDat[,obs], main=obs)
>  }
>
>  The pl list contains finally my desired result pl$x1 and pl$x2 are
>  different and show what I want it to. Now, the plots pl2$x1 and pl2$x2
>  are the same - they both show an x2 ~ x3 plot since this is the current
>  value of obs. So how can I force the variable name substitution? I tried
>  some combinations of parse/eval/substitute with no success.

In this case you are better off moving away from qplot (which does
various substitute tricks to assemble the named variables in a data
frame) to a more explicit form of ggplot:

pl2[[obs]] <- ggplot(cData, aes_string(x="x3", y=obs)) + geom_point()
+ opts(title = obs)

Hadley


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