How can I convert a boxed two-dimensional array to a two-dimensional string array in one step?

Question

Is there a way to convert a boxed two-dimensional array to a two-dimensional string array in one step using C#/.NET Framework 4.0?

using ( MSExcel.Application app = MSExcel.Application.CreateApplication() ) {
    MSExcel.Workbook book1 = app.Workbooks.Open( this.txtOpen_FilePath.Text );
    MSExcel.Worksheet sheet1 = (MSExcel.Worksheet)book1.Worksheets[1];
    MSExcel.Range range = sheet1.GetRange( "A1", "F13" );
    object value = range.Value; //the value is boxed two-dimensional array
}

I'm hopeful that some form of Array.ConvertAll might be made to work but so far the answer has eluded me.

Riggs

What is the actual type of value? Is it just Object[][]? – Soninlaw

According to the documentation, it is System.object: msdn.microsoft.com/en-us/library/… – Riggs

Sorry, I meant the runtime type, not the type of the property. If you call GetType() on that value, what is it? – Soninlaw

What is the result of value.GetType()? – Angrist

GetType() returns "System.Object[,]" for value. – Riggs

Answer 1

No, I do not think you can make the conversion in one step, but I might be wrong. But you can of course create a new array and copy from the old one to the new one:

object value = range.Value; //the value is boxed two-dimensional array
var excelArray = value as object[,];
var height = excelArray.GetLength(0);
var width = excelArray.GetLength(1);
var array = new string[width, height];
for (int i = 0; i < height; i++)
{
    for (int j = 0; j < width; j++)
        array[i, j] = excelArray[i, j] as string;
}

Edit:

Here is a two-dimensional overload of Array.ConvertAll which is not that much more complicated than the code above:

public static TOutput[,] ConvertAll<TInput, TOutput>(TInput[,] array, Converter<TInput, TOutput> converter)
{
    if (array == null)
    {
        throw new ArgumentNullException("array");
    }
    if (converter == null)
    {
        throw new ArgumentNullException("converter");
    }
    int height = array.GetLength(0);
    int width = array.GetLength(1);
    TOutput[,] localArray = new TOutput[width, height];
    for (int i = 0; i < height; i++)
    {
        for (int j = 0; j < width; j++)
            localArray[i, j] = converter(array[i, j]);
    }
    return localArray;
}

Mert

That was the approach I was going to resort to if I couldn't do it in one step. The intent is to use a built-in .NET function, if I can find one. Array.ConvertAll should be able to do it, according to its documentation, but I haven't been able to get it to work yet. – Riggs

Adding an idea I think you will like. – Mert

@Driver, according to the doc, ConvertAll() takes “ one-dimensional, zero-based Array”. – Angrist

This solution worked for me, but I did have to make a couple of changes. 1) The excelArray begins at [1,1], while the new array begins at [0,0]. Thus, I had to change one line in the for loop to account for this offset: array[i, j] = excelArray[i+1, j+1].ToString(); 2) height/width needed to be swapped in the line that creates the array: var array = new string[height, width]; Otherwise, this worked exactly as I needed--thanks! – Riggs

Glad I could help. These types of arrays are uncommon but they are supported by the framework. To handle the general case you would need to use GetLowerBound: msdn.microsoft.com/en-us/library/… – Mert

Answer 2

You can write your own ConvertAll for two-dimensional arrays:

public static TOutput[,] ConvertAll<TInput, TOutput>(
    this TInput[,] array, Func<TInput, TOutput> converter)
{
    int length0 = array.GetLength(0);
    int length1 = array.GetLength(1);

    var result = new TOutput[length0, length1];

    for (int i = 0; i < length0; i++)
        for (int j = 0; j < length1; j++)
            result[i, j] = converter(array[i, j]);

    return result;
}

Angrist

This is very close to what I'm looking for, but I had hoped that the .NET Framework by now includes something like this already. Array.ConvertAll starts complaining if I specify more than one dimension, which was surprising. – Riggs

Answer 3

string[][] strings = ((object[][])range.Value)
    .Select(x => x.Select(y => y.ToString()).ToArray()).ToArray();

Edit: The clarification about object[,] instead of object[][] obviously makes this approach obsolete. An interesting problem; multidimensional arrays are quite limited.

Fumikofumitory

Why in the world would you use AsQueryable here? – Leela

Ha. I think I got into that habit when I was first learning LINQ. It is quite silly, now that you mention it. Edited. – Fumikofumitory