Please Note: This article is written for users of the following Microsoft Excel versions: 2007, 2010, and 2013. If you are using an earlier version (Excel 2003 or earlier), this tip may not work for you. For a version of this tip written specifically for earlier versions of Excel, click here: Playing with a Full Deck.
by Allen Wyatt
(last updated December 5, 2017)
Excel is great at generating random numbers, but it is less great at filling a range of cells with random numbers in which no particular number is repeated twice. For instance, you might want to populate 52 cells with the numbers 1 through 52, in random order. (This is very similar to choosing cards from a deck in random order, where a particular card can only be chosen once. Thus the title for this tip.)
There obviously is no built-in Excel function to provide this capability, so you are left to work with macros. Fortunately, such a macro is not terribly difficult to create. The following macro will do the trick nicely:
Sub FillRand() Dim nums() As Integer Dim maxval As Integer Dim nrows As Integer, ncols As Integer Dim j As Integer, k As Integer Dim Ptr As Integer Randomize Set s = Selection maxval = s.Cells.Count nrows = s.Rows.Count ncols = s.Columns.Count ReDim nums(maxval, 2) 'Fill the initial array For j = 1 To maxval nums(j, 1) = j nums(j, 2) = Int((Rnd * maxval) + 1) Next j 'Sort the array based on the random numbers For j = 1 To maxval - 1 Ptr = j For k = j + 1 To maxval If nums(Ptr, 2) > nums(k, 2) Then Ptr = k Next k If Ptr <> j Then k = nums(Ptr, 1) nums(Ptr, 1) = nums(j, 1) nums(j, 1) = k k = nums(Ptr, 2) nums(Ptr, 2) = nums(j, 2) nums(j, 2) = k End If Next j 'Fill in the cells Ptr = 0 For j = 1 To nrows For k = 1 To ncols Ptr = Ptr + 1 s.Cells(j, k) = nums(Ptr, 1) Next k Next j End Sub
This macro uses a two-dimensional array (nums) to figure out which numbers to use and the order in which they should be used. Near the beginning of the macro the array is filled with a static number (1 through the number of cells) and a random number between 1 and the number of cells. This second number is then used to sort the array. Once the array is stored, it is a simple matter to place the original numbers in the cells.
By the way, the reason a two-dimensional array is used is because the Rnd function that VBA uses to generate random numbers can return duplicate values. Thus, even through the second dimension of the array can have duplicates in it, when the array is finally sorted, the first dimension will not have duplicates.
To use the macro, start by selecting the cells you want to have filled with sequential values in a random order. When you run the macro, that range is filled. For instance, if you select ten cells and then run the macro, then those cells are filled with the numbers 1 through 10, in random order.
ExcelTips is your source for cost-effective Microsoft Excel training. This tip (8269) applies to Microsoft Excel 2007, 2010, and 2013. You can find a version of this tip for the older menu interface of Excel here: Playing with a Full Deck.
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