Read multiple CSV files into separate data frames

问题

Suppose we have files file1.csv, file2.csv, ... , and file100.csv in directory C:\\R\\Data and we want to read them all into separate data frames (e.g. file1, file2, ... , and file100).

The reason for this is that, despite having similar names they have different file structures, so it is not that useful to have them in a list.

I could use lapply but that returns a single list containing 100 data frames. Instead I want these data frames in the Global Environment.

How do I read multiple files directly into the global environment? Or, alternatively, How do I unpack the contents of a list of data frames into it?

回答1:

Quick draft, untested:

Use list.files() aka dir() to dynamically generate your list of files.
This returns a vector, just run along the vector in a for loop.
Read the i-th file, then use assign() to place the content into a new variable file_i

That should do the trick for you.

回答2:

Thank you all for replying.

For completeness here is my final answer for loading any number of (tab) delimited files, in this case with 6 columns of data each where column 1 is characters, 2 is factor, and remainder numeric:

##Read files named xyz1111.csv, xyz2222.csv, etc.
filenames <- list.files(path="../Data/original_data",
    pattern="xyz+.*csv")

##Create list of data frame names without the ".csv" part 
names <-substr(filenames,1,7)

###Load all files
for(i in names){
    filepath <- file.path("../Data/original_data/",paste(i,".csv",sep=""))
    assign(i, read.delim(filepath,
    colClasses=c("character","factor",rep("numeric",4)),
    sep = "\t"))
}

回答3:

Use assign with a character variable containing the desired name of your data frame.

for(i in 1:100)
{
   oname = paste("file", i, sep="")
   assign(oname, read.csv(paste(oname, ".txt", sep="")))
}

回答4:

Here is a way to unpack a list of data.frames using just lapply

filenames <- list.files(path="../Data/original_data",
                        pattern="xyz+.*csv")

filelist <- lappy(filenames, read.csv)

#if necessary, assign names to data.frames
names(filelist) <- c("one","two","three")

#note the invisible function keeps lapply from spitting out the data.frames to the console

invisible(lapply(names(filelist), function(x) assign(x,filelist[[x]],envir=.GlobalEnv)))

回答5:

This answer is intended as a more useful complement to Hadley's answer.

While the OP specifically wanted each file read into their R workspace as a separate object, many other people naively landing on this question may think that that's what they want to do, when in fact they'd be better off reading the files into a single list of data frames.

So for the record, here's how you might do that.

#If the path is different than your working directory
# you'll need to set full.names = TRUE to get the full
# paths.
my_files <- list.files("path/to/files")

#Further arguments to read.csv can be passed in ...
all_csv <- lapply(my_files,read.csv,...)

#Set the name of each list element to its
# respective file name. Note full.names = FALSE to
# get only the file names, not the full path.
names(all_csv) <- gsub(".csv","",
                       list.files("path/to/files",full.names = FALSE),
                       fixed = TRUE)

Now any of the files can be referred to by my_files[["filename"]], which really isn't much worse that just having separate filename variables in your workspace, and often it is much more convenient.

回答6:

A simple way to access the elements of a list from the global environment is to attach the list. Note that this actually creates a new environment on the search path and copies the elements of your list into it, so you may want to remove the original list after attaching to prevent having two potentially different copies floating around.

回答7:

Reading all the CSV files from a folder and creating vactors same as the file names:

setwd("your path to folder where CSVs are")

filenames <- gsub("\\.csv$","", list.files(pattern="\\.csv$"))

for(i in filenames){
  assign(i, read.csv(paste(i, ".csv", sep="")))
}

回答8:

#copy all the files you want to read in R in your working directory
a <- dir()
#using lapply to remove the".csv" from the filename 
for(i in a){
list1 <- lapply(a, function(x) gsub(".csv","",x))
}
#Final step 
for(i in list1){
filepath <- file.path("../Data/original_data/..",paste(i,".csv",sep=""))
assign(i, read.csv(filepath))
}

来源：https://stackoverflow.com/questions/5319839/read-multiple-csv-files-into-separate-data-frames

标签

csv

file

lapply