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R Code Fragments
How can I read multiple files into R?

You may at times wish to read a set of data files into R.  The code below demonstrates how to do so looping through the names of the files to be read in.  We will show how to do this for all of the files in a single folder.  The datasets we read in here are from Stata, so we will be using the foreign package.

library(foreign)
setwd("D:/data/Stata data")
a<-list.files()
a

 [1] "charity.dta"  "spelling.dta" 
 
for (x in a) {
  u<-read.dta(x)
  usum<-summary(u[,1:3])
  print(usum)
}


      ta1              ta2              ta3        
 Min.   : 0.000   Min.   : 0.000   Min.   : 0.000  
 1st Qu.: 1.000   1st Qu.: 1.000   1st Qu.: 1.000  
 Median : 1.000   Median : 2.000   Median : 1.000  
 Mean   : 1.102   Mean   : 1.418   Mean   : 1.068  
 3rd Qu.: 2.000   3rd Qu.: 2.000   3rd Qu.: 1.000  
 Max.   : 3.000   Max.   : 3.000   Max.   : 3.000  
 NA's   :64.000   NA's   :37.000   NA's   :20.000  
      male           i1               i2        
 Min.   :0.0   Min.   :0.0000   Min.   :0.0000  
 1st Qu.:0.0   1st Qu.:0.0000   1st Qu.:0.0000  
 Median :0.5   Median :1.0000   Median :1.0000  
 Mean   :0.5   Mean   :0.5333   Mean   :0.5333  
 3rd Qu.:1.0   3rd Qu.:1.0000   3rd Qu.:1.0000  
 Max.   :1.0   Max.   :1.0000   Max.   :1.0000

The code above allows you to read in multiple files without typing in their names, but assumes you want all of the files in the working directory folder.  The code below allows you to list out the files you want to read.

library(foreign)
setwd("D:/data/Stata data")

for (x in c("charity.dta", "spelling.dta")) {
  u<-read.dta(x)
  usum<-summary(u[,1:3])
  print(usum)
}

      ta1              ta2              ta3        
 Min.   : 0.000   Min.   : 0.000   Min.   : 0.000  
 1st Qu.: 1.000   1st Qu.: 1.000   1st Qu.: 1.000  
 Median : 1.000   Median : 2.000   Median : 1.000  
 Mean   : 1.102   Mean   : 1.418   Mean   : 1.068  
 3rd Qu.: 2.000   3rd Qu.: 2.000   3rd Qu.: 1.000  
 Max.   : 3.000   Max.   : 3.000   Max.   : 3.000  
 NA's   :64.000   NA's   :37.000   NA's   :20.000  
      male           i1               i2        
 Min.   :0.0   Min.   :0.0000   Min.   :0.0000  
 1st Qu.:0.0   1st Qu.:0.0000   1st Qu.:0.0000  
 Median :0.5   Median :1.0000   Median :1.0000  
 Mean   :0.5   Mean   :0.5333   Mean   :0.5333  
 3rd Qu.:1.0   3rd Qu.:1.0000   3rd Qu.:1.0000  
 Max.   :1.0   Max.   :1.0000   Max.   :1.0000

Very similar code can be used for reading in multiple .csv files.

setwd("D:/data/")

for (x in c("diet.csv", "lsat.csv")) {
  u<-read.table(x, header = T, sep = ",")
  usum<-summary(u[,1:3])
  print(usum)
}
       id              t               c        
 Min.   :  1.0   Min.   :1.000   Min.   :7.470  
 1st Qu.:106.8   1st Qu.:1.000   1st Qu.:7.840  
 Median :208.5   Median :1.000   Median :7.940  
 Mean   :189.8   Mean   :1.185   Mean   :7.938  
 3rd Qu.:274.2   3rd Qu.:1.000   3rd Qu.:8.040  
 Max.   :337.0   Max.   :2.000   Max.   :8.390  
       id             item        wt2        
 Min.   : 1.00   Min.   :1   Min.   :  0.00  
 1st Qu.: 8.25   1st Qu.:2   1st Qu.:  3.00  
 Median :16.50   Median :3   Median : 11.00  
 Mean   :16.41   Mean   :3   Mean   : 30.52  
 3rd Qu.:24.00   3rd Qu.:4   3rd Qu.: 28.00  
 Max.   :32.00   Max.   :5   Max.   :298.00

If you have multiple datasets with the same sets of variables and you wish to append them to one long dataset, you can use the code below. Inside the loop, we create a variable indicating which dataset a given record came from.

setwd("D:/data/")

diet <- c()

for (x in c("diet1.csv", "diet2.csv")) {
  u<-read.table(x, header = T, sep = ",")
  u$dataset = x
  diet <- rbind(diet, u)
}

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