CODEWITHSUNDEEP
f#
Dymond
Dymond

Reputation: 2277

Write Array with List to csv

I have an array with multiple lists inside and want to write the values to an CSV unfortunately I cannot figure out how to write the Array.mapi.

Any ideas?

   let temp = [|title;body;ordinariePris;extraPris;inkopPris;images;allValues|]

   let lines2 = 
            temp 
            |> Array.mapi (fun idx (t,b,op,ep,ip,i,av) ->
                sprintf "%s\t%s\t%s\t%s\t%s\t%s\t%s\t%s" title body ordinariePris extraPris inkopPris images allValues
                       )
        let header = "title\tbody\tordinariePris\textraPris\tinkopPris\tallValues"
        
        System.IO.File.WriteAllLines("test.csv", 
            Array.append [| header|]lines2, Encoding.UTF8)

thanks in advance

Upvotes: 0

Views: 49

Answers (1)

Dan Barowy
Dan Barowy

Reputation: 2270

The problem with your code is that mapi indexes over the elements of temp, which means that you're only getting one column at a time. You want to retrieve one row at a time.

The following instead transposes your list of lists, so that indexing does what you want. It's also a little more generic-- you don't actually need to know the number of columns ahead of time. It does, however, assume that every column has the same number of elements in it.

let col1 = ["a"; "b"; "c"]
let col2 = ["1"; "2"; "3"]
let col3 = ["x"; "y"; "z"]

let cols = [col1; col2; col3]

let transpose(xs: string list list) : string list list =
  [0 .. xs.[0].Length - 1] |> List.map (fun i ->
    xs |> List.rev |> List.fold (fun acc col -> col.[i] :: acc) [] 
  )
  
let stringify_rows(xs: string list list) : string list =
  xs |> List.map (fun row -> System.String.Join(",", row))
  
System.IO.File.WriteAllLines("test.csv", cols |> transpose |> stringify_rows)

Note that this approach does not use an array of lists, since there was no obvious reason that you had to use an array. WriteAllLines will happily accept any IEnumerable.

If you do a lot of CSV writing, I recommend using a library like CsvHelper, since correctly handling when to quote or escape cell contents can be tricky.

Upvotes: 1

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