Dear R-users,
I am having a problem with passing an argument to a function in a do.call
function which itself is in a for statement.
I am building a function to upload question pools to the blackboard learning
environment.
This function which transforms questions to XML style output should be generic
and allow for any function to generate questions. Therefore I use do.call in
this function. However, because I make multiple versions of a single type of
item I use a for statement. Now, when specifying a path for a jpeg (which is
part of a question), this path is no longer found by the do.call statement when
it is in the for loop. Consequently no jpegs are being created (my created dirs
remain empty). I guess it has something to do with different environments
inside and outside the do.call. I don't know how to provide them to the do.call
properly. I tried to solve it by giving the path a `<<-' assignment but then
only one jpeg is being created the first time, all other jpegs are not created.
Maybe anyone of you can help?
Here is a simplified version of the code I have been using (looks a bit silly,
but the drawpic function is a bunch of code with all kinds of other
functionalities, which work fine).
#This function is unimportant; it generates random paths
randomstring<-function(a=1,n=31){
z<-vector(length=a)
for (h in 1:a){
x<-"n"
for (i in 1:n){
if (runif(1)>0.5){
y<-round(runif(1,-.5,9.5))
}
else {y<-letters[round(runif(1,.5,24.5))]
}
x<-paste(x,y, sep = "")
}
z[h]<-x }
z
}
#this is a simple function to generate jpegs
dp<-function(path){
jpeg(filename = path, width = 480, height = 480,
pointsize = 12, quality = 85, bg = "white",
res = NA, restoreConsole = TRUE)
x<-rnorm(1000)
hist(x)
dev.off()}
#this mimicks the generic function
drawpic<-function(method,methodArgs,rep=5){
dir.create(paste("C:\\BB\\"))
time<-format(Sys.time(), "%Y-%m-%d-%H%M")
dir.create(paste("C:\\BB\\",time,sep=""))
supdir<-paste("C:\\BB\\",time,sep="")
for (i in 1:rep){
subdir<-randomstring()
dir.create(paste(supdir,"\\",subdir,sep=""))
Path<<-paste(supdir,"\\",subdir,"\\jpg.jpg",sep="")#using `<-' instead of `<<-'
#does not produce any
pictures
x<-do.call(method,methodArgs)
}}
#run the small function within generic function:
drawpic(method=dp,methodArgs=list(path=Path))
Hope to hear from you people,
Cheers!
Dr Niels Smits
Taskforce Methods & Statistics
Faculty of Psychology and Education
Vrije Universiteit
The Netherlands
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