In This Chapter

• An overview of Excel’s data validation feature
• Practical examples of using data validation formulas

This chapter explores a useful Excel feature: data validation. Data validation enables you to add rules for what’s acceptable in specific cells and allows you to add dynamic elements to your worksheet without using macro programming.

About Data Validation

The Excel data validation feature allows you to set up rules that dictate what can be entered into a cell. For example, you may want to limit data entry in a particular cell to whole numbers between 1 and 12. You can specify an input message to help the user know what kind of data to enter in the cell. If the user makes an invalid entry, you can display a custom message. Figure 20.1 shows an example of both the input message and the message generated from an invalid entry.

Excel makes it easy to specify the validation criteria, and you can also use a formula for more complex criteria.

Specifying Validation Criteria

To specify the type of data allowable in a cell or range, follow these steps while you refer to Figure 20.2, which shows all three tabs of the Data Validation dialog box:

1. Select the cell or range.
2. Choose Data ➜ Data Tools ➜ Data Validation. Excel displays its Data Validation dialog box.
3. Click the Settings tab.
4. Choose an option from the Allow drop-down list. The contents of the Data Validation dialog box will change, displaying controls based on your choice. To specify a formula, select Custom.
5. Specify the conditions by using the displayed controls. Your selection in step 4 determines what other controls you can access.
6. (Optional) Click the Input Message tab and specify which message to display when a user selects the cell. You can use this optional step to tell the user what type of data is expected. If this step is omitted, no message will appear when the user selects the cell.

7. (Optional) Click the Error Alert tab and specify which error message to display when a user makes an invalid entry. The selection for Style determines what choices users have when they make invalid entries. To prevent an invalid entry, choose Stop. If this step is omitted, a standard message will appear if the user makes an invalid entry.

8. Click OK. The cell or range contains the validation criteria you specified.

Types of Validation Criteria You Can Apply

From the Settings tab of the Data Validation dialog box, you can specify a variety of data validation criteria. The following options are available from the Allow drop-down list. Keep in mind that the other controls on the Settings tab vary, depending on your choice from the Allow drop-down list.

• Any Value: Selecting this option removes any existing data validation. Note, however, that the input message, if any, still displays if the check box is selected on the Input Message tab.
• Whole Number: The user must enter a whole number. You specify a valid range of whole numbers by using the Data drop-down list. For example, you can specify that the entry must be a whole number greater than or equal to 100.
• Decimal: The user must enter a number. You specify a valid range of numbers by refining the criteria from choices in the Data drop-down list. For example, you can specify that the entry must be greater than or equal to 0 and less than or equal to 1.
• List: The user must choose from a list of entries you provide. This option is useful, and we discuss it in detail later in this chapter. (See “Creating a Drop-Down List.”)
• Date: The user must enter a date. You specify a valid date range from choices in the Data drop-down list. For example, you can specify that the entered data must be greater than or equal to January 1, 2016, and less than or equal to December 31, 2016.
• Time: The user must enter a time. You specify a valid time range from choices in the Data drop-down list. For example, you can specify that the entered data must be later than 12:00 p.m.
• Text Length: The length of the data (number of characters) is limited. You specify a valid length by using the Data drop-down list. For example, you can specify that the length of the entered data be 1 (a single alphanumeric character).
• Custom: To use this option, you must supply a logical formula that determines the validity of the user’s entry. (A logical formula returns either TRUE or FALSE.) You can enter the formula directly into the Formula control (which appears when you select the Custom option), or you can specify a cell reference that contains a formula. This chapter contains examples of useful formulas.

The Settings tab of the Data Validation dialog box contains two other check boxes:

• Ignore Blank: If selected, blank entries are allowed.
• Apply These Changes to All Other Cells with the Same Setting: If selected, the changes you make apply to all other cells that contain the original data validation criteria.

Creating a Drop-Down List

Perhaps one of the most common uses of data validation is to create a drop-down list in a cell. Figure 20.4 shows an example that uses the month names in A1:A12 as the list source.

To create a drop-down list in a cell, do the following:

1. Enter the list items into a single-row or single-column range. These items will appear in the drop-down list.
2. Select the cell that will contain the drop-down list and then access the Data Validation dialog box. (Choose Data ➜ Data Tools ➜ Data Validation.)
3. From the Settings tab, select the List option (from the Allow drop-down list) and specify the range that contains the list, using the Source control. The range can be in a different worksheet but must be in the same workbook.
4. Make sure that the In-Cell Dropdown check box is selected.
5. Set any other Data Validation options as desired.
6. Click OK. The cell displays an input message (if specified) and a drop-down arrow when it’s activated. Click the arrow and choose an item from the list that appears.

Using Formulas for Data Validation Rules

For simple data validation, the data validation feature is quite straightforward and easy to use. The real power of this feature, though, becomes apparent when you use data validation formulas.

We present several examples of formulas used for data validation in the upcoming section “Data Validation Formula Examples.”

Understanding Cell References

If the formula that you enter into the Data Validation dialog box contains a cell reference, that reference is considered a relative reference, based on the upper-left cell in the selected range.

The following example clarifies this concept. Suppose that you want to allow only an odd number to be entered into the range B2:B10. None of the Excel data validation rules can limit entry to odd numbers, so a formula is required.

Follow these steps:

1. Select the range (B2:B10 for this example) and ensure that cell B2 is the active cell.
2. Choose Data ➜ Data Tools ➜ Data Validation. The Data Validation dialog box appears.
3. Click the Settings tab and select Custom from the Allow drop-down list.

4. Enter the following formula in the Formula field, as shown in Figure 20.5:

   =ISODD(B2)

   This formula uses the ISODD function, which returns TRUE if its numeric argument is an odd number. Notice that the formula refers to the active cell, which is cell B2.

5. On the Error Alert tab, choose Stop for the Style and then type An odd number is required here as the error message.
6. Click OK to close the Data Validation dialog box.

Notice that the formula entered contains a reference to the upper-left cell in the selected range. This data validation formula was applied to a range of cells, so you might expect that each cell would contain the same data validation formula. Because you entered a relative cell reference as the argument for the ISODD function, Excel adjusts the formula for the other cells in the B2:B10 range. To demonstrate that the reference is relative, select cell B5 and examine its formula displayed in the Data Validation dialog box. You’ll see that the formula for this cell is

=ISODD(B5)

Generally, when entering a data validation formula for a range of cells, you use a reference to the active cell, which is normally the upper-left cell in the selected range. An exception is when you need to refer to a specific cell. For example, suppose that you select range A1:B10 and you want your data validation to allow only values that are greater than the value in cell C1. You would use this formula:

=A1>$C$1

In this case, the reference to cell C1 is an absolute reference; it will not be adjusted for the cells in the selected range, which is just what you want. The data validation formula for cell A2 looks like this:

=A2>$C$1

The relative cell reference is adjusted, but the absolute cell reference is not.

Data Validation Formula Examples

The following sections contain a few data validation examples that use a formula entered directly into the Formula control on the Settings tab of the Data Validation dialog box. These examples help you understand how to create your own data validation formulas.

=ISTEXT(A1)

=A2>A1

Accepting nonduplicate entries only

The following data validation formula does not permit the user to make a duplicate entry in the range A1:C20:

=COUNTIF($A$1:$C$20,A1)=1

This is a logical formula that returns TRUE if the value in the cell occurs only one time in the A1:C20 range. Otherwise, it returns FALSE, and the Duplicate Entry dialog box is displayed.

This formula assumes that A1 is the active cell in the selected range. Note that the first argument for COUNTIF is an absolute reference. The second argument is a relative reference, and it adjusts for each cell in the validation range. Figure 20.6 shows this validation criterion in effect, using a custom error alert message. The user is attempting to enter a value into cell B5 that already exists in the A1:C20 range.

=LEFT(A1)="a"

=EXACT(LEFT(A1,1),"a")

=COUNTIF(A1,"A????")=1

=WEEKDAY(A1)=2

Accepting only values that don’t exceed a total

Figure 20.7 shows a simple budget worksheet, with the budget item amounts in the range B1:B6. The planned budget is in cell E5, and the user is attempting to enter a value in cell B4 that would cause the total (cell E6) to exceed the budget. The following data validation formula ensures that the sum of the budget items does not exceed the budget:

=SUM($B$1:$B$6)<=$E$5

Creating a dependent list

As we described previously, you can use data validation to create a drop-down list in a cell (see “Creating a Drop-Down List”). This section explains how to use a drop-down list to control the entries that appear in a second drop-down list. In other words, the second drop-down list is dependent upon the value selected in the first drop-down list.

Figure 20.8 shows a simple example of a dependent list created by using data validation. Cell E2 contains data validation that displays a three-item list from the range A1:C1 (Vegetables, Fruits, and Meats). When the user chooses an item from the list, the second list (in cell F2) displays the appropriate items. Cell E2 contains data validation with its Allow criterion set to List and its Source criterion shown below:

=$A$1:$C$1

This worksheet uses three named ranges:

• Vegetables: A2:A15
• Fruits: B2:B9
• Meats: C2:C5

For this technique to work, your range names must match the values in A1:C1. For example, if you type Veggies in cell A1 and name the range Vegetables, the list in F2 won’t contain items. Cell F2 contains data validation that uses this formula:

=INDIRECT($E$2)

The INDIRECT function converts its argument into a range if it can. If cell E2 contains the text Fruits, for instance, INDIRECT looks for a range named Fruits and supplies that range to the data validation list.

Using Structured Table Referencing

With Excel Tables (Insert ➜ Table) you can use structured table referencing in your formulas. Figure 20.9 shows a simple table consisting of one column of names. You can create a formula like this one that matches a name to the list:

=MATCH("Joe",Table1[Name],FALSE)

The second argument, Table1[Name], is a structured reference that returns the Name column of the table named Table1. As you add or remove rows to that table, the structured reference adjusts and your formulas continue to work.

Unfortunately, you can’t use structured table references in your data validation criteria. To overcome this, you can create a named range that uses a structured table reference and use that name in your data validation.

To create a named range, choose Formulas ➜ Defined Names ➜ Define Name for the Ribbon. Enter the name, such as dvTable1Name, and point to the table’s column in the Refers To box. The reference changes to =Table1[Name], as shown in Figure 20.10.

Now you can use dvTable1Name in your data validation to get a list that grows or shrinks with the table. Figure 20.11 shows a cell with such validation.

This example used a naming convention of dv plus the table name plus the column name. You don’t have to use a convention like this; you can use any valid named range.