从R中的多个.csv文件读取，处理和导出分析结果

Question

I have a bunch of CSV files and I would like to perform the same analysis (in R) on the data within each file. Firstly, I assume each file must be read into R (as opposed to running a function on the CSV and providing output, like a sed script).

What is the best way to input numerous CSV files to R, in order to perform the analysis and then output separate results for each input?

Thanks (btw I'm a complete R newbie)

Answer 1

You could go for Sean's option, but it's going to lead to several problems:

1. You'll end up with a lot of unrelated objects in the environment, with the same name as the file they belong to. This is a problem because...
2. For loops can be pretty slow, and because you've got this big pile of unrelated objects, you're going to have to rely on for loops over the filenames for each subsequent piece of analysis - otherwise, how the heck are you going to remember what the objects are named so that you can call them?
3. Calling objects by pasting their names in as strings - which you'll have to do, because, again, your only record of what the object is called is in this list of strings - is a real pain. Have you ever tried to call an object when you can't write its name in the code? I have, and it's horrifying.

A better way of doing it might be with lapply() .

# List files
filelist <- list.files(pattern = "*.csv")

# Now we use lapply to perform a set of operations 
#   on each entry in the list of filenames.
to_dispose_of <- lapply(filelist, function(x) {

    # Read in the file specified by 'x' - an entry in filelist
    data.df <- read.csv(x, skip = 1, header = TRUE)

    # Store the filename, minus .csv. This will be important later.
    filename <- substr(x = x, start = 1, stop = (nchar(x)-4))

    # Your analysis work goes here. You only have to write it out once 
    #   to perform it on each individual file.
    ...

    # Eventually you'll end up with a data frame or a vector of analysis 
    #   to write out. Great! Since you've kept the value of x around, 
    #   you can do that trivially
    write.table(x = data_to_output, 
                file = paste0(filename, "_analysis.csv"), 
                sep = ",")
})

And done.

Answer 2

You can try the following codes by putting all csv files in the same directory.

names = list.files(pattern="*.csv")   %csv file names
for(i in 1:length(names)){ assign(names[i],read.csv(names[i],skip=1, header=TRUE))}

Hope this helps !