[R] ggplot2: mapping categorical variable to color aesthetic with faceting

baptiste auguie baptiste.auguie at googlemail.com
Tue Oct 6 18:36:52 CEST 2009


Hi,

I may be missing an important design decision, but could you not have
only a single data.frame as an argument of your function? From your
example, it seems that the colour can be mapped to the fac1 variable
of "data",

compareCats <- function(data) {

   require(ggplot2)
   p <- ggplot(data, aes(fac1, res, color=fac1)) + facet_grid(. ~ fac2)
   jit <- position_jitter(width = 0.1)
   p <- p + layer(geom = "jitter", position = jit) +
     scale_colour_manual(values=c("red", "blue"))
   print(p)
   }


test <- data.frame(res = rnorm(100), fac1 = as.factor(rep(c("A", "B"), 50)),
   fac2 = as.factor(rep(c("lrg", "lrg", "sm", "sm"), 25)))

compareCats(data = test)

rem <- runif(5, 1, 100) # randomly remove a few points here and there
last_plot() %+% test[-rem,] # replot with new dataset


HTH,

baptiste



2009/10/6 Bryan Hanson <hanson at depauw.edu>:
> Hello Again...  I¹m making a faceted plot of a response on two categorical
> variables using ggplot2 and having troubles with the coloring. Here is a
> sample that produces the desired plot:
>
> compareCats <- function(data, res, fac1, fac2, colors) {
>
>    require(ggplot2)
>    p <- ggplot(data, aes(fac1, res)) + facet_grid(. ~ fac2)
>    jit <- position_jitter(width = 0.1)
>    p <- p + layer(geom = "jitter", position = jit, color = colors)
>    print(p)
>    }
>
> test <- data.frame(res = rnorm(100), fac1 = as.factor(rep(c("A", "B"), 50)),
>    fac2 = as.factor(rep(c("lrg", "lrg", "sm", "sm"), 25)))
>
> compareCats(data = test, res = res, fac1 = fac1, fac2 = fac2, colors =
> c("red", "blue"))
>
> Now, if I get away from idealized data where there are the same number of
> data points per group (25 in this case), I run into problems.  So, if you
> do:
>
> rem <- runif(5, 1, 100) # randomly remove a few points here and there
> test <- test[-rem,]
> compareCats(data = test, res = res, fac1 = fac1, fac2 = fac2, colors =
> c("red", "blue"))
>
> R throws an error due to mismatch between the recycling of colors and the
> actual number of data points:
>
> Error in `[<-.data.frame`(`*tmp*`, gp, value = list(colour = c("red",  :
>  replacement element 1 has 2 rows, need 47
>
> I'm new to ggplot2, but have been through the book and the web site enough
> to know that my problem is "mapping the varible to the aesthetic"; I also
> know I can either "map" or "set" the colors.
>
> The question, finally:  is there an simple/elegant way to map a list of two
> colors corresponding to A and B onto any random sample size of A and B with
> faceting?  If not, and I must "set" the colors:  Do I compute the length of
> all possible combos of A, B with lrg, sm, and then create one long vector of
> colors for the entire plot?  I tried something like this, and was not
> successful, but perhaps could be with more work.
>
> All advice appreciated, Bryan (session info below)
>
> *************
> Bryan Hanson
> Professor of Chemistry & Biochemistry
> DePauw University, Greencastle IN USA
>
>> sessionInfo()
> R version 2.9.2 (2009-08-24)
> i386-apple-darwin8.11.1
>
> locale:
> en_US.UTF-8/en_US.UTF-8/C/C/en_US.UTF-8/en_US.UTF-8
>
> attached base packages:
> [1] grid      datasets  tools     utils     stats     graphics  grDevices
> methods
> [9] base
>
> other attached packages:
>  [1] ggplot2_0.8.3      reshape_0.8.3      proto_0.3-8        mvbutils_2.2.0
>  [5] ChemoSpec_1.1      lattice_0.17-25    mvoutlier_1.4      plyr_0.1.8
>  [9] RColorBrewer_1.0-2 chemometrics_0.4   som_0.3-4
> robustbase_0.4-5
> [13] rpart_3.1-45       pls_2.1-0          pcaPP_1.7          mvtnorm_0.9-7
> [17] nnet_7.2-48        mclust_3.2         MASS_7.2-48        lars_0.9-7
> [21] e1071_1.5-19       class_7.2-48
>
> ______________________________________________
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> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
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