R循环对多个csv文件执行功能

Question

I have tried to create a for loop that does something for each of 4 csv files similar to this but with more files.

dat1<- read.csv("female.csv", header =T)
dat2<- read.csv("male.csv", header =T)

for (i in 1:2) {
  message("Female, Male")
  Temp <- dat[i][(dat[i]$NAME == "Temp"), ]
  Temp <- Temp[complete.cases(Temp)]
  print(mean(Temp$MEAN))

However, I get an error:

Error in Temp$MEAN : $ operator is invalid for atomic vectors

Not sure why this isn't working. Any help would be appreciated for looping through csv files!

Answer 1

Personally, I think the easiest way to do this is with the plyr package:

library(plyr)
myFiles <- c("male.csv", "female.csv")
dat <- ldply(myFiles, read.csv)
dat <- dat[complete.cases(dat), ]
mean(dat$MEAN)

The way this works is that you first create a vector of file names. Then the ldply() function performs the function read.csv() on the vector of filenames, and converts the output automatically to a data.frame. Then you do the complete.cases() and mean() in the usual way.

Edit:

But if you want the mean of each file then here is one way of doing it:

# create a vector of files
myFiles <- c("male.csv", "female.csv")  

# create a function that properly handles ONLY ONE ELEMENT
readAndCalc <- function(x){            # pass in the filename
   tmp <- read.csv(x)                  # read the single file
   tmp <- tmp[complete.cases(tmp), ]   # complete.cases()
   mean(tmp$MEAN)                      # mean
}

x <- "male.csv"
readAndCalc(x)                         # test with ONE file

sapply(myFiles, readAndCalc)           # run with all your files

The way this works is that you first create a vector of filenames, just like before. Then you create a function that processes ONLY ONE file at a time. Then you can test that the function works using the readAndCalc function you just created. Finally do it for all your files with the sapply() function. Hope that helps.