R- for loop to select two columns in a data frame, with only the second column changing-CodePudding

I'm having issues trying to write a for loop in R. I have a dataframe of 16 columns and 94 rows and i want to loop through, selecting column 1, plus column 2 in one data frame, then col 1 col 3 etc, so i end up with 16 dataframes containing 2 columns, all written to individual .csv files

TwoB<- read.csv("data.csv", header=F) 

list<- lapply(1:nX, function(x) NULL)


nX <- ncol(TwoB)

for(i in 1:ncol(TwoB)){
list[[i]]<-subset(TwoB,
                 select=c(1, i 1))
 }

Which produces an error:

 Error in `[.data.frame`(x, r, vars, drop = drop): 
   undefined columns selected

I'm not really sure how to code this and clearly haven't quite grasped loops yet so any help would be appreciated!

CodePudding user response：

The error is easily explained as you loop over 16 columns and in the end trying to select 16 1 which column index does not exists. You probably could loop over nX-1 instead, but I think what you try to achieve can be done more elegant.

TwoB<- read.csv("data.csv", header=F)

library("data.table")
setDT(TwoB)

nX <- ncol(TwoB)

# example to directly write your files
lapply(2:nX, function(col_index) {
    fwrite(TwoB[, c(1, ..col_index)], file = paste0("col1_col", col_index, ".csv"))
})

# example to store the new data.tables in a list
list_of_two_column_tables <- lapply(2:nX, function(col_index) {
    TwoB[, c(1, ..col_index)]
})