Loading multiple files into matrix using R

问题:

I am new to the programming world and need help with loading a file to R and creating a matrix with it. I can import individual files and create and individual matrix out of it. How do I do this for multiple files? I have 21 files that each contain 100 rows and 100 columns and I need to import each file and put everything in a single array.

回答1:

1. I would use list.files to list my files by pattern.
2. lapply to loop through the list of files and create a list data.frame with read.csv

3. rbindlist to bind all in a big matrix.

   temp = list.files(pattern="*.csv")
   named.list <- lapply(temp, read.csv)
   library(data.table)
   files.matrix <-rbindlist(named.list)
   

回答2:

It's not exactly clear what structure you want. You can choose between a 2100x100 matrix or a 2100x100 dataframe or a 100x 100x 21 array or a list with 21 entries each of which was 100 x 100. (In R an array is the term one would use for a regular 3 dimensional structure with columns all of that same type. (and then of course there is agstudy's suggestion that you use a data.table.)

In a sense agstudy's code already gives you the 21 item list of dataframes each of dimension: 100x100:

temp = list.files(pattern="*.csv")
named.list <- lapply(temp, read.csv)

To get 100 x 100 x 21 array continue with this:

require(abind)
arr <- abind(named.list)

To get the 2100 x 100 dataframe, continue instead with:

longdf <- do.call(rbind, named.list)

To get the 2100 x 100 matrix continue from the last line with:

longmtx <- data.matrix(longdf)