Making Your Formulas Check for Errors in MS Excel

by Rekha 2010-02-24 15:31:42

One of the new worksheet functions introduced in Excel 2007 is the IFERROR function. The purpose of this function is to help simplify how you check for potential errors in your formulas. Consider a rather simple example:

=B8/B9

In most instances this formula will return a good result—unless cell B9 contains a zero value. In that case, Excel returns a #DIV/0! error. The traditional approach to trap this potentiality is to use the ISERROR function in this manner:

=IF(ISERROR(B8/B9),0,B8/B9)

The ISERROR function returns either True or False, depending on whether the expression being evaluated returns an error or not. The surrounding IF function can then act upon the value returned by ISERROR to determine what should be displayed.

The problem with this approach is that it is rather convoluted. Note, for instance, that your evaluation (B8/B9) needs to be included twice in the full formula. While that may not seem problematic with such a simple evaluation, with longer formulas it can be a real pain—at a minimum it makes your overall formula twice as long as it should be and provides two formulas that need to be kept in sync when you make changes.

This is where the new IFERROR function comes into play. It helps simplify the formulas you create. The following is the equivalent of the traditional formula presented earlier:

=IFERROR(B8/B9,0)

In this instance, the formula B8/B9 is evaluated and, if it results in an error, the 0 value is returned. If there is no error, then the value of the formula being evaluated is instead returned.

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