Write output of R loop to file

Question

Currently my R loop (see below) overwrites itself during each iteration. I want to output the result from each loop into a text file.

In more detail: R beginner here

Answer 1

To do it as the loop is running, in your loop add:

write.csv(data.frame(fname=filename[i],mean=mean),file="output.csv",append=TRUE)

However, this would mean a lot of file system overhead, and it would be quicker the produce the whole data frame in R and then write the file as a whole. So instead of your loop write:

means <- sapply(filename, function(x) mean(as.numeric(read.table(x,header=FALSE)$V4)))

And then write the file as a whole with:

write.csv(data.frame(fname=filename,mean=means),file="output.csv")