R-遍历文件列表

Question

I have a list of files with some data that I want to read in to R and then iterate over each file for some calculations. So far I was able to read the files with the following code:

METHOD1

filenames<-list.files(pattern="*.txt")
mynames<-gsub(".txt$", "", filenames)
for (i in 1:length(mynames)) assign(mynames[i], read.table(filenames[i]))

However when I try to apply some function to "names" it just says NULL

lapply(mynames,nrow)

I know that it could be easier to read the files directly into a list

METHOD2

temp<-list.files(pattern="*.txt")
myfiles<-lapply(temp, read.table,skip="#")

and then do lapply to that list lapply(myfiles,nrow) , but this just looses the information about which file produced each list.

Is there any way to circumvent this with either method in order to keep tracking the relation list-file?

Thanks

Answer 1

For method 2 you could easily use seomething like

temp <- list.files(pattern = "*.txt")
myfiles <- lapply(temp, read.table, skip = "#")
names(myfiles) <- temp

In this way the names attribute stores the filenames and you do not clutter your working environment with new variables.

So when you want to iterate over the content you can use lapply(myfiles, function(.) nrow(.)) or if you need to iterate over both the filename and the content you could so something like lapply(names(myfiles), function(.) nrow(myfiles[[.]]))

Answer 2

对于第一种方法，请尝试

  sapply(mynames,function(nameoffile){nrow(get(nameoffile))})