[R] ggplot2: proper use of facet_grid inside a function

[Bryan Hanson]

Hello Again R Folk:

I have found items about this in the archives, but I’m still not getting
it right.  I want to use ggplot2 with facet_grid inside a function with
user specified variables, for instance:

    p <- ggplot(data, aes_string(x = fac1, y = res)) + facet_grid(. ~
fac2)

Where data, fac1, fac2 and res are arguments to the function.  I have
tried

    p <- ggplot(data, aes_string(x = fac1, y = res)) + facet_grid(. ~
as.name(fac2))

and 

    p <- ggplot(data, aes_string(x = fac1, y = res)) + facet_grid(“. ~
fac2”)

But all of these produce the same error:

Error in `[.data.frame`(plot$data, , setdiff(cond, names(df)), drop =
FALSE) : 
  undefined columns selected

If I hardwire the true identity of fac2 into the function, it works as
desired, so I know this is a problem of connecting the name with the
proper value.

I'm up to date on everything:

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] Hmisc_3.6-0        ggplot2_0.8.3      reshape_0.8.3     
proto_0.3-8       
 [5] mvbutils_2.2.0     ChemoSpec_1.1      lattice_0.17-25   
mvoutlier_1.4     
 [9] plyr_0.1.8         RColorBrewer_1.0-2 chemometrics_0.4   som_0.3-4 
       
[13] robustbase_0.4-5   rpart_3.1-45       pls_2.1-0          pcaPP_1.7 
       
[17] mvtnorm_0.9-7      nnet_7.2-48        mclust_3.2        
MASS_7.2-48       
[21] lars_0.9-7         e1071_1.5-19       class_7.2-48      

loaded via a namespace (and not attached):
[1] cluster_1.12.0

Thanks for any help!  Bryan
*************
Bryan Hanson
Professor of Chemistry & Biochemistry
DePauw University, Greencastle IN USA