Cleaning Up Lists

Larry works for a firm that does outbound calls to potential customers. The firm has downloaded the national Do-Not-Call list, and wants to check their targeted phone numbers against the list, so they can make sure they don't call anyone that is on the DNC list. He was wondering how this can be done in Excel.

First of all, the natural question is whether Excel is even the proper tool to use for such a task. In checking information at the Federal Trade Commission's Web site, it appears that the DNC list, which is a flat text file, can consist of either phone numbers in individual area codes or a file that contains all area codes. Quick calculations indicate that the average area code list has in excess of 300,000 phone numbers, with over 120,000,000 phone numbers nationwide.

Working with such large quantities of phone numbers in Excel is not only impractical, but virtually impossible--Excel will only handle up to 65,536 rows of data. A better solution would be to use some sort of database program (perhaps Access), which can work with much larger numbers of records. You could also search the Web for proprietary solutions that will work with the DNC list.

Assuming that you work with just a subset of the DNC list, and that it will all fit within your copy of Excel, then it is a relatively easy task to compare one list against another. This assumes that the data in your DNC list and the "need to check" list are in the same text format. For the sake of this example, assume as well that the DNC list is in column A, and the "need to check" list is in column C. You can then follow these steps:

1. Select the cell in column D that is just to the right of the first phone number you want to check in column C.
2. Enter the following formula in the selected cell:

     =ISNA(MATCH(C2,$A:$A,0))

The results of the formula indicate whether the adjoining phone number is in the DNC list or not. If the result is TRUE, then the phone number is not in the DNC list; a result of FALSE means it is in the DNC list and should not be called. At this point you can easily sort the "need to check" list according to the results of the formula in column D. You can then delete all the phone numbers for which the value in column D is FALSE.

ExcelTips is your source for cost-effective Microsoft Excel training. This tip (2319) applies to Microsoft Excel 97, 2000, 2002, and 2003.