Limiting Input to a Format

As you are developing a spreadsheet, you may want to limit what users are able to put into a particular cell. For instance, you might want to make sure that entries in a cell are exactly four characters long, begin with the number 6, are followed by any digit, then by a letter, and then by any digit.

There are three ways to go about such a validation. The first, of course, is to write a macro that will check input and ensure that the entries follow the desired pattern. The way to concoct such a macro has been covered in other issues of ExcelTips.

Another method, without using macros, is to rely upon the data validation feature of Excel. If the number of valid entries is not terribly long, you might try these general steps:

1. On a blank worksheet, construct a list of the valid entries.
2. On the worksheet used for input, highlight the cell into which the entry will be made.
3. Choose Validation from the Data menu. Excel displays the Data Validation dialog box. (Click here to see a related figure.) To display the dialog box in Excel 2007 display the Data tab of the ribbon and click Data Validation in the Data Tools group.
4. Using the Allow drop-down list, choose List.
5. With the insertion point in the Source box, choose the list you put together in step 1.
6. Click on OK.

Now, whenever someone tries to enter data that is not included in your list of acceptable values, the validation rules kick into effect and the user is forced to change the entry.

You can also use the data validation feature in a bit of a different way. If you have well-defined rules for your data entry then you can put together a formula that describes a valid entry. The following is one such formula:

=AND((LEN(A1)=4),(LEFT(A1,1)="6"),(ISNUMBER(VALUE(
(MID(A1,2,1))))),(CODE(MID(UPPER(A1),3,1))>64),(CODE(
MID(UPPER(A1),3,1))<91),(ISNUMBER(VALUE((MID(A1,4,1))))))

Remember that this is a single formula, entered all on one line, using the following general steps:

1. Highlight the cell into which the entry will be made. (The above formula assumes you are using cell A1. If a different cell is selected, you will need to make the appropriate reference changes to the above formula.)
2. Choose Validation from the Data menu. Excel displays the Data Validation dialog box. (To display the dialog box in Excel 2007 display the Data tab of the ribbon and click Data Validation in the Data Tools group.)
3. Using the Allow drop-down list, choose Custom.
4. Enter the above formula in the Formula box. (All one line, no spaces.)
5. Click on OK.

You may get an error when you click on OK, based on the contents of A1. (Excel may try to tell you that the contents of A1 don't validate according to the rule.) This is OK; the validation rule you are setting up will come into play when someone tries to enter something in the cell.

The formula basically pulls apart the entry being made and determines if each character is within bounds. If not, then the result of the formula is FALSE, and the validation rules come into play.