Usually, when you specify a range in a formula, you specify it through its address: for example, $B$5:$C$10. However, you can specify ranges through formulae, effectively making them dynamic.
There are a number of formulae you can use to specify dynamic ranges, including OFFSET and IF.
Using the OFFSET formula to define a dynamic range
The formula that is most often used to define a dynamic range is OFFSET. The result of an OFFSET formula is a range. You have to specify the top left hand corner and the dimensions.
Specifically, there are five arguments:
- Reference: A range that forms the basis of the new range. This can be a single cell, or a range of adjacent cells.
- Rows: The number of rows up (negative) or down (positive) from the top of the reference range that you want the new range to start at.
- Cols: The number of columns left (negative) or right (positive) from the left of the reference range that you want the new range to start at.
- Height: The height (number of rows) of the new range. This argument is optional. If you omit it, the new range will have the same number of rows as the reference range.
- Width: The width (number of colums) of the new range. This argument is optional. If you omit it, the new range will have the same number of columns as the reference range.
So, for example, the result of the formula OFFSET($B$5:$C$10, 3, -1) would be the range A8:B13: it starts 3 rows down and one column to the left of B5, and has 6 rows and 2 columns, just like the range $B$5:$C$10.
The real utility of this formula comes when you use formulae for some of the arguments, and define a name to refer to it.
For example, suppose you have monthly sales data in a spreadsheet; you want to plot a chart, but don’t want to edit the chart each time you update the sales data.
You can define a name SalesData to refer to the following formula:
=OFFSET(chartData!$B$5,0,0,COUNT(chartData!C:C)-COUNT(chartData!$B$1:$B$4),1)
and then set the data series in the chart to refer to SalesData.
You can then update the chart simply by adding a new line of data.
Note that we have to be a bit careful how we specify the number of rows in the dynamic range, so as not to count any values that are not sales data.
Using IF to define a dynamic range
There is an even simpler way to define a dynamic range, which is especially useful for data validation. Suppose you have related sets of options: if you choose a service level of premier, for example, you can choose one of three delivery methods, but if the service level is standard, you only have a choice of two.
For the cell B5 we can set the data validation type to list and enter the following formula as the range:
=IF($B$4="Premier", $E$3:$E$5,$E$4:$E$5)
The drop down box for cell B5 will then show the valid delivery options for the service level chosen in cell B4.