Question

Two functions are defined:

let to2DStrArray (inObj : string[][]) = 
    Array2D.init   inObj.Length inObj.[0].Length (fun i j -> inObj.[i].[j])                            

let toTypedList typeFunc (strArray : string[,]) =
    if (Array2D.length1 strArray) = 0 then 
        []
    else
        List.init (Array2D.length1 strArray) typeFunc

trying to call them from fsx as follows fails:

    let testData = to2DStrArray [|[||]|] 
    let failingCall =   testData
                        |> toTypedList (fun row -> (Double.Parse(testData.[row,0]),
                                    Double.Parse(testData.[row,1])))

What is a working/better way to get this code to handle the case of empty 2-dimensional string arrays?

Answer 1

The problem is not in toTypeList function so you don’t have to check whether strArray is empty or not. It will give an error if you check inObj.[0].Length in to2DStrArray function when the input array is empty. A safe way to create an Array2D from an array of array is using array2D operator:

let to2DStrArray (inObj : string[][]) =
    array2D inObj

Of course, you have to guarantee that all inner arrays have the same length. And the other function is shortened as follows:

let toTypedList typeFunc (strArray : string[,]) =
    List.init (Array2D.length1 strArray) typeFunc

Given your use case, note that [|[||]|] is not an empty string[][]; it is an array which consists of only one element which in turn is an empty string array. Therefore, it causes a problem for the anonymous function you passed to toTypedList. Since the two dimensional array has length2 <= 1 and you accesses two first indices, it results in an index of bound exception. The function could be fixed by returning option values, and you can extract values from option values to use later on:

let testData = to2DStrArray [|[||]|] 
let failingCall = testData                    
                  |> toTypedList (fun row -> if Array2D.length2 testData >= 2 then Some (Double.Parse(testData.[row,0]), Double.Parse(testData.[row,1])) else None)