将多维数组转换为具有可空值的单个数组

Question

I am using ExcelDNA/C#/Excel primarily. What I am essentially trying to do is convert a multi-dimensional array (namely a range of cells) to a singular dimensional array, using the following code:

private static string[] MultiToSingle(object[,] multiArray)
{
   List<string> tempList;
   string[] returnArray;
   tempList = new List<string>();

   //Add each element of the multi-dimensional Array to the list
   foreach (object oneObj in multiArray)
   {
      tempList.Add(oneObj.ToString());
   }
   //Convert the list to a single dimensional array
   returnArray = tempList.ToArray();
   return returnArray;
}

This works a treat, and is used a number of times throughout my project, however I would like to add some more functionality.

When I try to run this function with a range that contains an empty cell, it errors horribly, at the moment I just have a try/catch with an error message informing the user to enter N/A into any empty cells.

What I'd really like to do, is in this function perhaps, convert any 'null' or whatever Excel stores empty cells as to the text string "N/A".

Answer 1

Perhaps just:

tempList.Add(oneObj == null ? "n/a" : oneObj.ToString());

I can also think of ways to make it more efficient, if you want:

string[] arr = new string[multiArray.Length];
int i = 0;
foreach (object oneObj in multiArray)
{
    arr[i++] = oneObj == null ? "n/a" : oneObj.ToString();
}
return arr;

This cuts out the intermediate list and a few backing array copies.

Answer 2

If you're finding nulls, which is probably why you're getting an error, Marc's answer is right. But you might like to use the function in another context - directly as a worksheet function exposed by Excel-DNA.

Excel-DNA marshals empty Excel cells into the argument array as objects of type ExcelDna.Integration.ExcelEmpty. So if your code is called directly from Excel-DNA as a worksheet function, you'd get the type name from the ToString(), and not an error.

So your function with the return type changed to object[] (Excel-DNA won't register your string[] function directly) looks like this:

public static object[] MultiToSingle(object[,] multiArray)
{
   List<string> tempList;
   object[] returnArray;
   tempList = new List<string>();

   //Add each element of the multi-dimensional Array to the list
   foreach (object oneObj in multiArray)
   {
      tempList.Add(oneObj.ToString());
   }
   //Convert the list to a single dimensional array
   returnArray = tempList.ToArray();
   return returnArray;
}

and gives this output in Excel when called directly as a worksheet function:

For this case you could add a check on the type of the array item to deal with empty cells:

 tempList.Add( oneObj is ExcelEmpty ? "!EMPTY" : oneObj.ToString() ); 

Answer 3

tempList.Add( oneObj.Value == null ? "!EMPTY" : oneObj.ToString() );