Create multiple lattice plots using for

Question

I'm trying to generate multiple plots using a lattice command, as follows:

variable <- (string with variable names)

for (i in 1:X){

 mypath <- paste(i,' - ',variable[i],'.png',sep='')
 png(mypath,width=760)

  xyplot(get(variable[i]) ~ GroupVariable, groups = IDvariable,
         data = dataset,
         type = "l" )

 dev.off()
}

The problem is, although the individual piece of code works fine, when executing the for loop the files are generated without any plot. The code works fine with other plots not generated by lattice. Does anyone know how to fix this?

Regards, David

Answer 1

print(xyplot(...)) should help

The lattice function xyplot() does not produce any output when it is called in another function (i.e. a for loop). Hence, in a loop the output of xyplot() has to be printed in in an extra step.

I had the same problem and this post explained everything: https://stat.ethz.ch/pipermail/r-help/2005-May/071467.html

To solve your problem you have to put the xyplot() call inside print(). Your code example should work like this:

variable <- (string with variable names)

for (i in 1:X){

 mypath <- paste(i,' - ',variable[i],'.png',sep='')
 png(mypath,width=760)

 print(xyplot(get(variable[i]) ~ GroupVariable, groups = IDvariable,
        data = dataset,
        type = "l"))
 dev.off()
}

Answer 2

Wrapping the operations in a function with lapply for index traversal is a scalable solution. facet_grid from ggplot provides alternative plotting scheme.

Note usage of aes_string for usage with string variables and as.formula to contruct dynamic formulae.

data(mtcars)

library("lattice")
library("ggplot2")


 fn_exportPlot = function(
 dataObj = mtcars, 
 indepVar  = "cyl", 
 depVar = "mpg",
 groupVar = "am",
 plotEngine=c("lattice","ggplot")) {

filePath =  paste0(indepVar,"_",plotEngine,'.png')

png(filePath,width=760) 


if(plotEngine=="lattice"){ 

formulaVar = as.formula(paste0(depVar," ~ ",indepVar,"|",groupVar))

 print(xyplot(formulaVar,data=dataObj))

}else{

 groupForm = as.formula(paste0("~ ",groupVar))

 gg = ggplot(mtcars,aes_string(indepVar,depVar)) + geom_point(shape=1) + facet_grid(groupForm)

 print(gg)


}

dev.off()


}

varList = c("cyl","disp")

lapply(varList,function(x) fn_exportPlot(indepVar = x,plotEngine="lattice") )
lapply(varList,function(x) fn_exportPlot(indepVar = x,plotEngine="ggplot") )

Plots: