Don't use assign(), named lists are much better (check the stuff on
indexing lists). Here's an example:
a <- list()
a[["one"]] <- c(1,2,3)
a[["two"]] <- c(4,5,6)
a[["two"]]
do.call("rbind",a)
do.call("cbind",a)
lapply(a,sum)With regards to your question, did you try printing varname[i] in your loop to see which value causes the error message? > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Koen Hufkens > Sent: Wednesday, November 23, 2005 7:37 AM > To: R help mailinglist > Subject: [R] assign() problem > > > I've written a piece of code (see below) to do a wavelet image > decomposition, during the evaluation of this code I would > like to write > the results of some calculations back to the R root directory. I used > assign() to do so because the names should vary when going thrue a > while() loop. For some unknown reason I get an error that says: > > Error in assign(varname[i], imwrImage) : > invalid first argument > > what could be wrong, when I do it on the commandline everything works > out just fine. But within the function it doesn't. When I disable the > assign statement, everything runs fine so the rest of the > code should be > clean. > > My code: > > # Wavelet multiresolution decomposition > > wmra <- function(image_file){ > #require(rimage) > require(wavethresh) > > #reading image file and converting it to grayscale > #dimage <- read.jpeg(image_file) > #dimage <- imagematrix(dimage) > > # discrete wavelet decomposition > imwdImage <- imwd(image_file) > > # get a value for the number of decomposition levels > #nlevels <- imwdImage$nlevels > > i <- 0 > varname <- paste("level",0:(imwdImage$nlevels-1),sep="") > print(varname) > while ( i < imwdImage$nlevels) > { > > # set the threshold to 0 on all levels except the one > in evaluation > # thresholdLevels is the list of levels to set to zero > thresholdLevels <- 1:(imwdImage$nlevels-1) > thresholdLevels[i] <- 0 > thresholdedCoeff <- > threshold.imwd(imwdImage,levels=thresholdLevels, > policy=c("manual"), type="hard", value=10000) > > # calculate the inverse wavelet transform > imwrImage <- imwr(thresholdedCoeff) > > # assign the various decomposition level data a name > # starting at i+1 because i = 0. > assign(varname[i+1],imwrImage) # --> gives an error > > # export the multiresolution decomposition for level i as graph > jpeg(paste("level",i,".jpg",sep=""),quality=100) > image(imwrImage,xlab=c("MRA image of level: > ",i),col=gray(255:0/256)) > dev.off() > > i <- i + 1 > } > > } > > Best regards, Koen > > ______________________________________________ > R-help@stat.math.ethz.ch mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide! > http://www.R-project.org/posting-guide.html > ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
