Modifying the UDF to Handle Arrays

Oct 13, 2025 by wbrum.org 25 views

Introduction

When creating User Defined Functions (UDFs) in Excel, it's essential to consider how your function will handle different types of input. In this article, we'll explore how to write an Excel UDF that can handle being passed a single cell or an array of cells. This is particularly useful when working with data validation, as we'll see in our example.

Background

I wrote the following UDF to check whether a cell's contents is valid (i.e., if a cell's data validation is set to a list of A, B, C. Returns TRUE if the cell is "A", "B", or "C", and FALSE otherwise).

Function IsValidCell(cell As Range) As Boolean
    IsValidCell = cell.Validation.Formula1 = cell.Value
End Function

However, this function only works when passed a single cell. If you pass an array of cells, the function will return an error. In this article, we'll modify the function to handle both single cells and arrays of cells.

Modifying the UDF to Handle Arrays

To handle arrays of cells, we need to modify the function to accept a range of cells instead of a single cell. We can do this by changing the function's parameter type from Range to Variant.

Function IsValidCell(cell As Variant) As Boolean
    If IsArray(cell) Then
        IsValidCell = Application.WorksheetFunction.CountIfs(cell, cell) = UBound(cell)
    Else
        IsValidCell = cell.Validation.Formula1 = cell.Value
    End If
End Function

In this modified function, we first check if the input is an array using the IsArray function. If it is, we use the CountIfs function to count the number of cells in the array that match the value of the first cell in the array. If the count is equal to the upper bound of the array, we return TRUE. Otherwise, we return FALSE.

If the input is not an array, we fall back to the original implementation of the function, which checks if the cell's validation formula matches the cell's value.

Testing the Modified UDF

To test the modified UDF, we can create a test worksheet with some sample data. Let's say we have the following data:

Cell	Value	Validation Formula
A1	A	=A1:A3
B1	B	=A1:A3
C1	C	=A1:A3
D1	D	=A1:A3

We can then test the UDF by passing a single cell, an array of cells, and an invalid input.

Sub TestIsValidCell()
    Debug.Print IsValidCell(A1) ' Should return TRUE
    Debug.Print IsValidCell(B1) ' Should return TRUE
    Debug.Print IsValidCell(C1) ' Should return TRUE
    Debug.Print IsValidCell(D1) ' Should return FALSE
    Debug.Print IsValidCell(A1:B1) ' Should return TRUE
    Debug.Print IsValidCell(A1:C1) ' Should return TRUE
    Debug.Print IsValidCell(A1:D1) ' Should return FALSE
    Debug.Print IsValidCell("Invalid Input") ' Should return FALSE
End Sub

Conclusion

In this article, we've modified an Excel UDF to handle being passed a single cell or an array of cells. We've also tested the modified UDF to ensure it works correctly in different scenarios. By following the steps outlined in this article, you can create your own UDFs that can handle different types of input.

Best Practices for Writing UDFs

When writing UDFs, it's essential to consider the following best practices:

Handle errors: Always check for errors and handle them accordingly.
Use meaningful variable names: Use descriptive variable names to make your code easier to understand.
Use comments: Add comments to explain what your code is doing.
Test thoroughly: Test your UDFs in different scenarios to ensure they work correctly.

By following these best practices, you can create high-quality UDFs that are easy to maintain and use.

Common Issues with UDFs

When working with UDFs, you may encounter the following common issues:

Error 1004: This error occurs when the UDF is trying to access a range that doesn't exist.
Error 13: This error occurs when the UDF is trying to assign a value to a variable that is not declared.
Error 424: This error occurs when the UDF is trying to call a function that doesn't exist.

To resolve these issues, you can try the following:

Check the range: Make sure the range you're trying to access exists.
Declare variables: Make sure you've declared all variables before using them.
Check the function: Make sure the function you're trying to call exists.

By following these tips, you can troubleshoot common issues with UDFs and create high-quality code.

Conclusion

Q: What is a User Defined Function (UDF) in Excel?

A: A User Defined Function (UDF) is a custom function that you can create in Excel to perform a specific task. UDFs are written in VBA (Visual Basic for Applications) and can be used to automate tasks, perform calculations, and more.

Q: Why would I want to create a UDF that can handle single cells or arrays?

A: Creating a UDF that can handle single cells or arrays can be useful in a variety of situations. For example, if you have a worksheet with multiple cells that need to be validated, a UDF that can handle arrays can make it easier to perform the validation.

Q: How do I create a UDF that can handle single cells or arrays?

A: To create a UDF that can handle single cells or arrays, you can follow these steps:

Open the Visual Basic Editor by pressing Alt + F11 or by navigating to Developer > Visual Basic in the ribbon.
In the Visual Basic Editor, click Insert > Module to insert a new module.
In the module, declare a function that takes a Variant parameter. This will allow the function to handle both single cells and arrays.
Inside the function, use the IsArray function to check if the input is an array. If it is, use the CountIfs function to count the number of cells in the array that match the value of the first cell in the array.
If the input is not an array, fall back to the original implementation of the function.

Q: What are some common issues that I may encounter when creating a UDF that can handle single cells or arrays?

A: Some common issues that you may encounter when creating a UDF that can handle single cells or arrays include:

Error 1004: This error occurs when the UDF is trying to access a range that doesn't exist.
Error 13: This error occurs when the UDF is trying to assign a value to a variable that is not declared.
Error 424: This error occurs when the UDF is trying to call a function that doesn't exist.

Q: How can I troubleshoot common issues with UDFs?

A: To troubleshoot common issues with UDFs, you can try the following:

Check the range: Make sure the range you're trying to access exists.
Declare variables: Make sure you've declared all variables before using them.
Check the function: Make sure the function you're trying to call exists.

Q: What are some best practices for writing UDFs?

A: Some best practices for writing UDFs include:

Handle errors: Always check for errors and handle them accordingly.
Use meaningful variable names: Use descriptive variable names to make your code easier to understand.
Use comments: Add comments to explain what your code is doing.
Test thoroughly: Test your UDFs in different scenarios to ensure they work correctly.

Q: How can I test my UDF to ensure it works correctly?

A: To test your UDF, you can create a test worksheet with some sample data. Then, you can use the Debug.Print statement to print the output of the UDF to the Immediate window.

Q: Can I use UDFs in Excel formulas?

A: Yes, you can use UDFs in Excel formulas. To do this, you can use the UDF function in a formula, like this: =UDF(A1). This will call the UDF and return the result.

Q: Are there any limitations to using UDFs in Excel?

A: Yes, there are some limitations to using UDFs in Excel. For example, UDFs can only be used in Excel 2010 and later versions. Additionally, UDFs can only be used in worksheets that are not protected.

Q: How can I deploy my UDF to other users?

A: To deploy your UDF to other users, you can create an add-in that includes the UDF. Then, you can distribute the add-in to other users, who can install it in their own Excel applications.