R循环对多个csv文件执行功能 [英] R loop perform function on multiple csv files

问题描述

我已经尝试创建一个for循环，为4个csv文件中的每个文件类似，但是有更多的文件。

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))

b $ b

但是，我得到一个错误：

However, I get an error:

错误：$ MEAN：$ operator对原子向量无效

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

不知道为什么这不工作。

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

推荐答案

我个人认为，最简单的方法是使用plyr package：

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)

这种方式的工作原理是首先创建一个文件名的向量。然后ldply（）函数对文件名的向量执行函数read.csv（），并将输出自动转换为data.frame。

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.

编辑：

但是如果你想要每个文件的平均值，这里是一个方法：

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

你首先创建一个文件名的向量，就像以前一样。然后创建一个只处理一个文件的函数。然后你可以使用刚刚创建的readAndCalc函数来测试函数是否工作。最后，使用sapply（）函数为所有文件执行此操作。希望有帮助。

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.

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