Skip null values in seq<Nullable<int>> in FSharp.Charting

Question

I have seq<Nullable<int>> and need to create nice plot, but without null values. Here is my code:

open System
#r """..\packages\FSharp.Charting.0.90.14\lib\net40\FSharp.Charting.dll"""
#load """..\packages\FSharp.Charting.0.90.14\FSharp.Charting.fsx"""
open FSharp.Charting

//in a real world replaced by .csv with empty values
let seqWithNullInt = seq[Nullable 10 ; Nullable 20  ; Nullable (); Nullable 40; Nullable 50] 
//let seqWithNullInt = seq[ 10 ; 20  ;  30;  40; 50]  //works fine

let bothSeq = seqWithNullInt |> Seq.zip {1..5}

Chart.Line bothSeq // Error because of nullable int 

And here is my vision:

How to skip null values? I don't want to replace them by nearest or something, I need to skip them from chart.. Is there any solution?

Answer 1

Something like this might work (note that I've used Option values instead of nullables, since that's more idiomatic in F#):

let neitherPairHasNoneInValue (pair1, pair2) =
    pair1 |> snd |> Option.isSome && pair2 |> snd |> Option.isSome
let seqWithNone = Seq.ofList [Some 10; Some 20; None; Some 40; Some 50]
let pairsWithoutNone = seqWithNone
                       |> Seq.zip {1..5}
                       |> Seq.pairwise
                       |> Seq.filter neitherPairHasNoneInValue
printfn "%A" pairsWithoutNone

This will output [(1,10),(2,20) ; (4,40),(5,50)]. I don't know the FSharp.Charting API offhand so I can't tell you which function will take that list of X,Y pairs and draw the graph you want, but it should be relatively straightforward to get from there to your graph.