How can I create a function or a loop over dataframe names in R?

Question

I'm a new programmer and I'm stuck with the creation of a function or loop to avoid repetition of the lines.

Here is part of my code:

# Importing dataframes
R1 <- read.table("C:/Users/Data1.txt", header = TRUE)
R2 <- read.table("C:/Users/Data2.txt", header = TRUE)
R3 <- read.table("C:/Users/Data3.txt", header = TRUE)

# Taking only the colunms that I need from each dataframe
R1_dados <- R1[,c(1,8,11,14,24)]
R2_dados <- R2[,c(1,8,11,14,24)]
R3_dados <- R3[,c(1,8,11,14,24)]

# Adding some colunms 
R1_dados$E <- c(0,100,200,300,400,500,600)
R2_dados$E <- c(0,100,200,300,400,500,600)
R3_dados$E <- c(0,100,200,300,400,500,600)

# Doing some math between columns from each dataframe
R1_dados$rETR = R1_dados$fvfm*R1_dados$E
R2_dados$rETR = R2_dados$fvfm*R2_dados$E
R3_dados$rETR = R3_dados$fvfm*R3_dados$E

# and so on...

I was wondering if I can create an index of the replicas (R1, R2, and R3)

I'll be grateful if someone helps me. Thanks!

If the operations are so similar you could store R1 - R3 in a list and then each operation becomes a simple lapply. Something like: R_list <- list(R1, R2, R3); R_list_dados <- lapply(R_list, "[", c(1,8,11,14,24); R_list_dados2 <- lapply(R_list_dados, function(x) x$E <- c(0,100,200,300,400,500,600)) and so on — Mike H.
– Mike H., Commented Dec 5, 2017 at 16:18
See How do I make a list of data frames for some discussion and examples. — Gregor Thomas
– Gregor Thomas, Commented Dec 5, 2017 at 16:36
Yes, I do need to keep R1, R2... In addition, later in the code, I need to create a column with different values to each one. — CS3420
– CS3420, Commented Dec 5, 2017 at 18:27

Emmanuel-Lin · Accepted Answer · 2017-12-05 16:20:30Z

1

You should loop on a file list.

fileList <- c("Data1", "Data2", "Data3")
for (file in fileList){
  R <- read.table(paste0("C:/Users/", file, ".csv"))
  R_dados <- R[,c(1,8,11,14,24)]
  R_dados$E <- c(0,100,200,300,400,500,600)
  R_dados$rETR = R_dados$fvfm*R3_dados$E
  write.table(R_dados, file = paste0("C:/Users/", file, "_dados.csv"))
}

answered Dec 5, 2017 at 16:20

Emmanuel-Lin

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3 Comments

Nate Over a year ago

I agree with @Emmanuel-Lin. Also, if you don't want to create a new output file but just want to import them into a single datafram, you can initialize the dataframe with df <- NULL if you have options(stringsAsFactors=F) and append to df using rbind().

CS3420 Over a year ago

It works, but I need to keep the index to include other values to each one.

Emmanuel-Lin Over a year ago

By index you mean 1,2,3.. from Data1, Data2, Data3... ? If so parse your file name to get it

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