Randomly assign data to groups
To randomly people (or anything) to groups you can use the RANDBETWEEN function with the CHOOSE function. In the example shown, the formula in F3 is:
When copied down the column, this formula will generate a random group (A, B, or C) for each person in the list.
Note: this is a random approach that will allow groups of difference sizes. If you need a formula approach to randomly assign people to groups of a fixed size, see this formula and this video overview.
How this formula works
The RANDBETWEEN function generates random numbers between two integers. The CHOOSE function takes a number as the first argument, and uses that number to select the "nth" item from the following arguments.
So, in this formula, RANDBETWEEN generates a number between 1 and 3, this number is used to choose a group from the 3 following values: "A","B","C".
You can use this same approach any time you need make random assignments. It's especially useful when you you need to assign data to a limited number of text values.
Be aware that RANDBETWEEN will re-calculate whenever there is any change to a workbook, or even when a workbook is opened. Once you have a set of random assignments, you may want to copy and paste the formulas as values to prevent further changes.