Trying to merge multiple csv files in R

问题:

I'm attempting to merge multiple csv files using R. all of the CSV files have the same fields and are all a shared folder only containing these CSV files. I've attempted to do it using the following code:

multmerge=function(mypath) {
    filenames=list.files(path=mypath, full.names=TRUE)
    datalist= lapply(filenames, function (x) read.csv(file=x, header=True))
    Reduce(function(x,y) merge(x,y), datalist)}

I am entering my path as something like "Y:/R Practice/specdata". I do get an ouput when I apply the function to my 300 or so csv files, but the result gives me my columns names, but beneath it has <0 rows> (or 0-length row.names). Please let me know if you have any suggestions on why this isn't working and how I can fix it.

回答1:

For a shorter, faster solution

library(dplyr)
library(readr)
df <- list.files(full.names = TRUE) %>% 
  lapply(read_csv) %>% 
  bind_rows 

回答2:

Your code worked for me, but you need change header = True to header = TRUE.

回答3:

If all your csv files have exactly the same fields (column names) and you want simply to combine them vertically, you should use rbind instead of merge:

> a
             A         B
[1,]  2.471202 38.949232
[2,] 16.935362  6.343694
> b
            A          B
[1,] 0.704630  0.1132538
[2,] 4.477572 11.8869057
> rbind(a, b)
             A          B
[1,]  2.471202 38.9492316
[2,] 16.935362  6.3436939
[3,]  0.704630  0.1132538
[4,]  4.477572 11.8869057

回答4:

Another option that has proved to work for my setup:

multmerge = function(path){
  filenames=list.files(path=path, full.names=TRUE)
  rbindlist(lapply(filenames, fread))
}


path <- "Dropbox/rstudio-share/dataset/MB"
DF <- multmerge(path)

If you need a much granular control of your CSV file during the loading process you can change the fread by a function like so:

multmerge = function(path){
  filenames=list.files(path=path, full.names=TRUE)
  rbindlist(lapply(filenames, function(x){read.csv(x, stringsAsFactors = F, sep=';')}))
}