Accessing entries in a csv files for computation F#

arrays, csv, f#, math

Solution

What I do is create a record type so I can use strongly typed operations lateron, and then read the textfile into a `seq<myRecord>` very quickly like this code below. If i intend to reuse this lateron I usually move the method to the record as `static member fromFile`. The seq is very useful if you work with large textfiles as I do usually, it uses very little memory this way.

edit this is cleaner:

open System.IO

type myRecord = { 
    Visits: int
    Count: int 
} with
    static member fromFile file = 
        file
        |> File.ReadLines       // expose as seq<string>
        |> Seq.skip 1           // skip headers
        |> Seq.map (fun s-> s.Split '\t') // split each line into array
        |> Seq.map (fun a -> {Visits=int a.[0]; Count=int a.[1]}) // and create record

myRecord.fromFile @"D:\data.csv"
|> Seq.fold (fun (tv, tc) r -> (tv+r.Visits*r.Count, tc+r.Count))(0,0)
|> (fun t -> float (fst t) / float (snd t))
//val mean : float = 2.866666667

Problem

How can I access the entries in a csv file in order to perform calculations on them in F#? I can read the csv file into memory in the usual way, but once there I am stuck. Ideally I would just create arrays from the columns and then use array.map2 to perform calculations. So I array 1 is some website usage metric, and column 2 is the number of users that reached the value in column 1 (say made 6 visits to a website) we could calculate the mean number of visits by multiplying each entry in an array of column 1, by an array made from column 2 and dividing by the array.sum of column 2. I have tried the csv to Array code on F# snippets, http://fssnip.net/3T, but it produces and array for me that is a series of string tuples. Can anyone suggest a better approach? EDIT: Some sample input would be similar to this:- ``` Visits Count 1 8 2 9 3 5 4 3 5 2 6 1 7 1 10 1 ``` And the output would be to return the mean of the data, in this case 2.87 (to 2 decimal places). EDIT 2: The current output from the CSV to array code I found is this ``` val it : seq<BookWindow> = seq [{Visits = 1; Count = 8;}; {Visits = 2; Count = 9;}; {Visits = 3; Count = 5;}; {Visits = 4; Count = 3;}; ...] ``` which is not so useful for calculations...

Original source