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COMMENTS

Welcome to the fourth issue of the Excel Experts E-letter (or EEE), by 
David Hager. EEE is a semi-monthly publication. Feel free to distribute
copies of EEE to your friends and colleagues. 

Again, I have selected a theme for this issue. This time it is dealing 
with unique items in a dataset.

Remember that EEE is devoted to sharing ideas across the Excel developer
community, so if you have some great Excel technique that is not well-
known, send it to me and I will include it in a future issue.

For back issues of EEE, check out:
http://www.j-walk.com/ss/excel/eee/index.htm

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TOP EXCEL WEB SITES

There is a wealth of information at the following site.

http://www.baarns.com/IE4/index_devonly.asp

However, new material has not been added in quite some time.

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WORKSHEET FORMULA TIPS

Created by David Hager

This array formula returns the number of unique items in a worksheet
range.

=SUM(1/COUNTIF(Rng,Rng))

However, if Rng contains blank cells, this formula returns an error. In
this case, use this modified version of the formula.

=SUM(COUNTIF(Rng,Rng)/IF(NOT(COUNTIF(Rng,Rng)),1,COUNTIF(Rng,Rng))^2)



Created by David Hager

This array formula returns the Nth largest unique value in a column range.

=LARGE(IF(MATCH(Rng,Rng,0)=ROW(Rng)-MIN(ROW(Rng))+1,Rng,""),N)


Created by David Hager

To apply data validation to a column which allows only unique items to be
entered, highlight that column and select (in Excel 97 and later versions)
Data, Validation from the menu. Choose the custom option and enter the 
following formula (for column A):

=COUNTIF($A$1:A1,A1)=1

Created by Laurent Longre

This formula counts the number of unique items a column range, only if the 
cells in the lookup range contain the specified string. 

=SUM(N(FREQUENCY(IF(lookupRange="specifStr",MATCH(colRange,colRange,0)),
MATCH(colRange,colRange,0))>0))


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POWER FORMULA TECHNIQUE

Created by David Hager, Bob Umlas and Laurent Longre

The problem - to create an array containing only the unique items from an
expanding column list. In other words, if items are typed down column A,
what is the formula that will return the unique items? The following example
further illustrates the problem.
 
ColA
a
b
1
b
3

In this case, the array should be {"a";"b";1;3}. Then, if additional values
are added:

a
b
1
b
3
c
1
d
a
b

the array should be {"a";"b";1;3;"c";"d"}. The answer to this problem has
eluded me for years, but with recent input from Bob and Laurent, I have
successfully constructed a solution to this problem. The formula is somewhat
long, so it is necessary to define parts of the formula to simplify the 
final form.


Define TheList as:

=OFFSET(Sheet1!$A$1,,,COUNTA(Sheet1!$A:$A),)

This formula creates the expanding range for the items as they are entered
into column A.

Define sArray as:

=SMALL(IF(MATCH(TheList,TheList,0)=ROW(TheList),ROW(TheList),""),
ROW(INDIRECT("1:"&SUM(N(MATCH(TheList,TheList,0)=ROW(TheList))))))-1

This formula contains several important elements that require explanation.
The formula IF(MATCH(TheList,TheList,0)=ROW(TheList),ROW(TheList),"") 
returns an array of positions for the unique items that is the same size as
the TheList array, where the duplicates items are now represented by empty 
strings. The formula ROW(INDIRECT("1:"&SUM(N(MATCH(TheList,TheList,0)=ROW(
TheList))))) returns an array of numbers from 1 to n, where n is the number 
of unique items in the list, as calculated by the formula SUM(N(MATCH(TheList
,TheList,0)=ROW(TheList))). What is desired is an array that contains the 
unique positions with no empty strings. This is accomplished by the use of 
the SMALL function which, along with the LARGE function, is unique among 
Excel functions in its ability to create different sized arrays than the 
array used in the 1st argument if the 2nd argument is also an array. The -1 
is used to adjust the item positions for use in the formula shown below.

Define TheUniqueArray as:

=IF(T(OFFSET(TheList,sArray,,1))="",N(OFFSET(TheList,sArray,,1)),
T(OFFSET(TheList,sArray,,1)))

The formula OFFSET(TheList,sArray,,1) is an array of single element arrays, 
as explained in detail in the 1st issue of EEE. It can be converted into a
normal array by using the N or T functions. Both N and T are used here since
TheList can contain either text or numeric items. 

WARNING: ALTHOUGH THIS TECHNIQUE WORKS, IT MUST NOT BE APPLIED TO SITUATIONS
WHERE THERE ARE LARGE ARRAYS (>1000 ITEMS). EXCEL'S CALCULATION ENGINE RUNS
MUCH TOO SLOWLY ON THIS TYPE OF FORMULA. FOR EXAMPLE, IT CALCULATES ~100
TIMES SLOWER THAN THE PROGRAMMING TECHNIQUES FOR COUNTING UNIQUE ITEMS THAT
ARE SHOWN BELOW FOR AN ARRAY OF 5000 ITEMS.


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VBA CODE EXAMPLES 

Here are four examples of counting unique values in a list. Each of these
examples creates an array of the unique items, so they can be modified to
to those arrays for a purpose other than just counting the unique items.

Created by David Hager 

Sub cMethodAdvFilter()
    CountUniqueByAdvFilter Selection.Address
End Sub

Sub CountUniqueByAdvFilter(mRange As String)
    Dim TheRange As String
    Application.ScreenUpdating = False
    
    TheRange = "'[" & ActiveWorkbook.Name & _
    "]" & ActiveSheet.Name & "'!" & mRange
    
    Workbooks.Add
    
    Range(TheRange).AdvancedFilter Action:=xlFilterCopy, CopyToRange _
	:=Range("A1"), Unique:=True
    
    MsgBox Application.WorksheetFunction.CountA(Range("A:A"))
    
    ActiveWorkbook.Close False
    
    Application.ScreenUpdating = True
End Sub


Created by Keyuan Jiang 

    Sub cMethodDAO()
    Dim strDBFullName As String
    Dim dbData As Database, rstWork As Recordset, strSQL As String

    strDBFullName = ThisWorkbook.Path & "\" & ThisWorkbook.Name

    strSQL = "select distinct [your_field] from dataarea"
    
    'Appropriate driver needed for this statement

    Set dbData = OpenDatabase(strDBFullName, False, True, _
	"Excel8.0;HDR=YES;")

    Set rstWork = dbData.OpenRecordset(strSQL)

    rstWork.MoveLast 
   
    MsgBox rstWork.RecordCount

    Set rstWork = Nothing    
    Set dbData = Nothing
    End Sub

where [your_field] is the header of the column you are interested in and
the dataarea is a named area that contains all data in question (could be 
the single column you are interested in).


By David Hager

Sub CountUniqueByPivotTable()

    On Error GoTo uOut

    Application.ScreenUpdating = False
    Application.DisplayAlerts = False

    TheHeader = ActiveCell.Value

    ActiveSheet.PivotTableWizard SourceType:=xlDatabase, _
    SourceData:=ActiveSheet.Name & "!" & _
    Selection.Address, TableDestination:="", TableName:="uPivotTable"
 
    ActiveSheet.PivotTables("uPivotTable").AddFields RowFields:=TheHeader

    ActiveSheet.PivotTables("uPivotTable").PivotFields(TheHeader). _
    Orientation = xlDataField

    MsgBox Application.WorksheetFunction.CountA(Range("a:a")) - 3

    ActiveSheet.Delete

    Application.ScreenUpdating = True
    Application.DisplayAlerts = True

    Exit Sub
uOut:
    Application.ScreenUpdating = True
    Application.DisplayAlerts = True
End Sub


By John Walkenbach 

Sub cMethodByCollection()
    CountUniqueByCollection Selection.Address
End Sub

Sub CountUniqueByCollection(AllCells As String)

    Dim NoDupes As New Collection

    On Error Resume Next

    For Each Cell In Range(AllCells)

        NoDupes.Add Cell.Value, CStr(Cell.Value)

	'Note: the 2nd argument (key) for the Add method must be a string

    Next Cell 
  
    On Error GoTo 0

End Sub

Although not tested extensively, it appears that the procedure that uses 
the Collection object produces the fastest result. 


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EXCEL 2000 TIP

Under Tools, Options, View there is a checkbox entitled "Windows in Taskbar".
When it is checked, every file/window that is open in Excel has its own
Taskbar button. Uncheck that box if you do not want this feature. Under
View, Toolbars, Customize, Options there is a checkbox entitled "Menus show 
recently used commands first". When it is checked, menu items change their 
position based how often they are used. Uncheck that box if you do not want 
this feature.

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DID YOU KNOW?...

that the Office Spreadsheet Component can have up to 676 columns.

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Issue No.4 OF EEE (PUBLISHED 30Apr1999)
Next issue scheduled for 16MAY1999.
BY David Hager
dchager@compuserve.com