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.

Playing with a Full Deck

by Allen Wyatt
(last updated September 28, 2013)

3

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.

Author Bio

Allen Wyatt

With more than 50 non-fiction books and numerous magazine articles to his credit, Allen Wyatt is an internationally recognized author. He  is president of Sharon Parq Associates, a computer and publishing services company. ...

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Comments

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What is 6 - 3?

2016-01-09 10:56:53

Rick Rothstein

I don't know if Thomas or Bryan will still be following replies to this blog article or not, but I believe the following macro (which I just posted to Allen Wyatt's other blog article referenced in the "Please Note" box at the top of this blog article) will be faster (untested claim) than Allen Wyatt's code no matter what sorting method was used because my code does not use any sorting whatsoever.

Sub FillRand()
Dim X As Long, RandIndex As Long, Nums As Variant, Cell As Range
Randomize
Nums = Evaluate("TRANSPOSE(ROW(1:" & Selection.Count & "))")
For Each Cell In Selection
RandIndex = Int((UBound(Nums) - X) * Rnd + 1)
Cell.Value = Nums(RandIndex)
Nums(RandIndex) = Nums(UBound(Nums) - X)
X = X + 1
Next
End Sub

Note: This macro will work in XL2003 or later for sure... it may work in earlier versions as well, but XL2003 is the earliest version I own, so I cannot be sure about earlier versions.


2013-09-30 10:01:31

Bryan

Thomas, Allen's solution is actually relatively simple and it's the exact same principal as yours; the difference is the internal Excel sorting method is faster than Allen's. This makes me sad, because his method is more "proper"; I'm guessing, however, that with a more advanced sorting algorithm you could get the times to approach each other.

CPearson has a method that is even faster than using the worksheet to sort (http://www.cpearson.com/excel/SortingArrays.aspx) I tested all 4 methods and here are the results I got with 7,700 values to sort:

Allen Sort: 30.4057
Wrksht Sort: 0.3405
CPrson Sort: 0.1668


With something more reasonable (52, since we are talking cards), the time difference is negligible:

Allen Sort: 0.0015
Wrksht Sort: 0.0738
CPrson Sort: 0.0005

This time the worksheet sorting solution is actually the slowest!


2013-09-28 14:52:43

Thomas Papavasiliou

The proposed method works OK but I think that it is rather complicated.

A simpler and much faster way is to insert two new columns in A and B and fill the first new column A, with a sequence of numbers from 1 to the number of cells in the selection, place next to it, that is the second inserted column B the formula =rand() and fill it down.
Then sort the two new columns having B as key and cutting the sorted A column, to slices equal to the number of rows of the selection and moving them to the selection.

A trial with some 550 rows and 14 columns, run on my PC approximately seven times faster.

If anybody is interested in this version I will be pleased to provide it


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