AutoFill with Random Numbers

Excel includes a feature that allows you to automatically fill a range of cells with information you have placed in just a few cells. For instance, you could enter the value 1 in a cell, and then 2 in the cell just beneath it. If you then select the two cells and drag the small black handle at the bottom right corner of the selection, you can fill any number of cells with incrementing numbers. This AutoFill feature sure beats having to type in all the values!

You may wonder if there is a similar way to use the AutoFill feature to place random numbers in a range. Unfortunately, the AutoFill feature was never meant for random numbers. Why? Because AutoFill uses predictive calculations to determine what to enter into a range of cells. For example, if you entered 1 into one cell and 5 into the next, highlighted the cells and then used AutoFill, the next number entered in the cell below would be 9 because Excel can deduce that the increment is 4. It is a constant increment that can be predicted.

Random numbers on the other hand are, well, random. By nature, they cannot be predicted, else they wouldn't be random. Therefore, the predictive nature of AutoFill cannot be applied to random numbers.

However, there are ways around this. One is to simply use the various formulas (using RAND and RANDBETWEEN) that have already been adequately covered in other issues of ExcelTips. These formulas can quickly and easily be copied over a range of cells, using a variety of copying techniques.

Another approach is to use a feature of the Analysis ToolPak which makes putting random numbers into a range of cells pretty easy. Just follow these steps:

1. Display the Data tab of the ribbon.
2. Click Data Analysis in the Analysis group. Excel displays the Data Analysis dialog box. (See Figure 1.)



Figure 1. The Data Analysis dialog box.

3. In the list of functions in the dialog box, choose Random Number Generation.
4. Click on OK. Excel displays the Random Number Generation dialog box. (See Figure 2.)



Figure 2. The Random Number Generation dialog box.

5. Using the controls in the dialog box, indicate the parameters you want used in generating a range of random numbers. (Make sure that you specify a range of cells in the Output Options area of the dialog box.)
6. Click on OK.

You can find a good explanation of all the dialog box options (step 5) at this website:

https://www.bettersolutions.com/excel/EUN147/YI231420881.htm

If you don't see the Analysis group on the Data tab of the ribbon (step 2), it means that you don't have the Analysis ToolPak enabled. Follow these steps to enable it:

1. Display the Excel Options dialog box. (In Excel 2007 click the Office button and then click Excel Options. In Excel 2010 and later versions display the File tab of the ribbon and then click Options.)
2. At the left side of the dialog box click Add-Ins.
3. At the bottom of the dialog box use the Manage drop-down list to select Excel Add-ins.
4. Click the Go button. Excel displays the Add-Ins dialog box. (See Figure 3.)



Figure 3. The Add-Ins dialog box.

5. Select the check box next to Analysis ToolPak.
6. Click OK.

The Analysis group should now appear on the Data tab of the ribbon. When you use the Random Number Generation tool, you might be a bit overwhelmed by all the options it provides you.

ExcelTips is your source for cost-effective Microsoft Excel training. This tip (8810) applies to Microsoft Excel 2007, 2010, 2013, 2016, 2019, and 2021. You can find a version of this tip for the older menu interface of Excel here: AutoFill with Random Numbers.