There are actually 2 dates,the 24th and the 25th, in the data sample. You can do this in a manner that's both fairly comprehensible and succint, for arbitrary

There are actually 2 dates,the 24th and the 25th, in the data sample. You can do this in a manner that's both fairly comprehensible and succint, for arbitrary number of dates, using a Json TypeProvider in F#. #r @"../Fsharp.Data.dll" open FSharp.Data open System type PersonsData = JsonProvider<"../data.sample.json"> let dateTriple (d:PersonsData.Root) = d.Timestamp.Year, d.Timestamp.Month,d.Timestamp.Day let info = PersonsData.Load ("./data.json") let uniqueDates = info |> Array.map dateTriple |> set let createCsv (d : PersonsData.Root seq) = d |> Seq.filter (fun p -> Option.isSome p.Creditcard) |> Seq.map (fun p -> sprintf "%s,%s" p.Name p.Creditcard.Value ) |> String.concat "\n" info |> Seq.groupBy dateTriple |> Seq.iter (fun ((y,m,d), data) -> IO.File.WriteAllText (sprintf "%d%02d%02d.csv" y m d, createCsv data)) With the below as a sample (though dataset itself could have been used since it's not so large): [{"name":"Quincy Gerhold","email":"laron.cremin@macejkovic.info","city":"Port Tiabury","mac":"64:d2:17:ff:28:13","timestamp":"2015-04-25 15:57:12 +0700","creditcard":null},{"name":"Lolita Hudson","email":"tracy.goodwin@schmidt.com","city":"Port Brookefurt","mac":"2d:20:78:41:8e:35","timestamp":"2015-04-25 23:20:21 +0700","creditcard":"1211-1221-1234-2201"}]