for loop in list.files function produces result only for the last i (R)

Question

I have a directory that contains lets say two .csv files, that i want to read and import into R.

So far i have tried the code below that actually works. But only for one of the files.

for (i in list.files(path = ".", pattern = "\\.csv$")){
    print(i)
    f <- read.table(i, fill=TRUE, row.names=NULL)
    Table <- data.frame(f[3])
    Table["station.id"] <- i
}
Table

Produces

      V3 station.id
1   8.27  agrin.csv
2   9.11  agrin.csv
3  11.60  agrin.csv
4  15.30  agrin.csv
5  20.53  agrin.csv
6  25.07  agrin.csv
7  27.42  agrin.csv
8  27.11  agrin.csv
9  22.92  agrin.csv
10 17.98  agrin.csv
11 13.15  agrin.csv
12  9.62  agrin.csv
13 17.34  agrin.csv

What i want is to implement a for loop that will iterate the dir and create a table as shown above for each file inside.

Notice that print(i) line gives back two results agrin.csv and agr.csv for example

Any suggestions?

Answer 1

Before the for loop, let:

 Table <- data.frame(V3=numeric(0), station.id=character(0))

This is called object preallocation. Then, in the loop, try playing with rbind. With this scheme you'll be creating your object incrementally.

Answer 2

You are not specifying the row index of Table$station.id so the last value ends up being written over the whole column. Try this:

file.names <- list.files(path = ".", pattern = "\\.csv$")
Table <- data.frame(V3=rep(NA, length(file.names)), 
                    station.id=rep(NA, length(file.names)))
for (i in seq_along(file.names)){
    print(file.names[i])
    f <- read.table(file.names[i], fill=TRUE, row.names=NULL)
    Table[i, "V3"] <- f[3]     ## this only works if f has only one observation.
    Table[i, "station.id"] <- file.names[i]
}
Table