CSV spreadsheet files are suitable for storing tabular data in a relatively portable way.

The CSV format is flexible but somewhat ill-defined.

For present purposes, authors may assume that the data fields contain no commas, backslashes, or quotation marks.



Task

Read a CSV file, change some values and save the changes back to a file.

For this task we will use the following CSV file:

C1,C2,C3,C4,C5
1,5,9,13,17
2,6,10,14,18
3,7,11,15,19
4,8,12,16,20

Suggestions


 Show how to add a column, headed 'SUM', of the sums of the rows.
 If possible, illustrate the use of built-in or standard functions, methods, or libraries, that handle generic CSV files.



open System.IO
 
[<EntryPoint>]
let main _ =
    let input = File.ReadAllLines "test_in.csv"
    let output = 
        input
        |> Array.mapi (fun i line -> 
            if i = 0 then line + ",SUM" 
            else
                let sum = Array.sumBy int (line.Split(','))
                sprintf "%s,%i" line sum)
    File.WriteAllLines ("test_out.csv", output)
    0
 