nandeshwar.info » UDF

Student’s t-test for equal means

admin — Wed, 29 Oct 2008 13:06:00 +0000

If you do not wish to enter complex formula in Excel and you already have calculated average, count, and variance for your samples(Tip:use a PivotTable), then you can use these user-defined functions to calculate the t-test stat value and degrees of freedom required to do hypothesis testing. Both the functions provide an optional argument for the assumption of equal variances; by default it is set to false.

Here’s the code for t-test:

'---------------------------------------------------------------------------------------
' Procedure : TTESTM
' DateTime  : 10/29/2008 08:35
' Author    :
' Purpose   : To get the t-stat value when comparing two means with an optional input
'               for equal or unequal variances
'               by default the function assumes that the user is comparing means with unequal variances
' davg1 is the mean of first sample
' dcnt1 is the sample size of sample 1 
' dvar1 is the variance of first samaple 
' davg2 is the mean of second sample
' dcnt2 is the sample size of sample 2 
' dvar2 is the variance of second samaple 
' blnEqVar set TRUE to assume equal variance for the test
'---------------------------------------------------------------------------------------

Public Function TTESTM(davg1 As Double, dcnt1 As Double, dvar1 As Double, davg2 As Double, dcnt2 As Double, dvar2 As Double, Optional blnEqVar As Boolean = False) As Double
 
On Error GoTo TTESTM_Error
Dim dResult As Double, dNumer As Double, dDenon As Double, dPooledVar As Double
 
dNumer = davg1 - davg2
 
'if equal variances are not assumed
'http://www.itl.nist.gov/div898/handbook/eda/section3/eda353.htm
If Not blnEqVar Then
	dDenon = Sqr((dvar1 ^ 2 / dcnt1) + (dvar2 ^ 2 / dcnt2))
Else
'if equal variances are assumed, then calculated the pooled variance
	dPooledVar = Sqr((((dcnt1 - 1) * dvar1 ^ 2) + ((dcnt2 - 1) * dvar2 ^ 2)) / (dcnt1 + dcnt2 - 2))
	dDenon = dPooledVar * Sqr((1 / dcnt1) + (1 / dcnt2))
End If
 
dResult = dNumer / dDenon
 
TTESTM = dResult
Exit Function
 
TTESTM_Error:
	TTESTM = Null
 
End Function

Code for degrees of freedom

'---------------------------------------------------------------------------------------
' Procedure : DOFTTESTM
' DateTime  : 10/29/2008 08:50
' Author    :
' Purpose   : To get the degrees of freedom for the t-test when comparing two means with an optional input
'               for equal or unequal variances
'               by default the function assumes that the user is comparing means with unequal variances

' dcnt1 is the sample size of sample 1 
' dvar1 is the variance of first samaple 
' dcnt2 is the sample size of sample 2 
' dvar2 is the variance of second samaple 
' blnEqVar set TRUE to assume equal variance for the test
'---------------------------------------------------------------------------------------
'
Public Function DOFTTESTM(dcnt1 As Double, dvar1 As Double, dcnt2 As Double, dvar2 As Double, Optional blnEqVar As Boolean = False) As Double
 
Dim dResult As Double, dNumer As Double, dDenon As Double
 
On Error GoTo DOFTTESTM_Error
'if equal variances are not assumed, then use a complicated formula to compute degrees of freedom
'http://www.itl.nist.gov/div898/handbook/eda/section3/eda353.htm
If Not blnEqVar Then
	dNumer = ((dvar1 ^ 2 / dcnt1) + (dvar2 ^ 2 / dcnt2)) ^ 2
	dDenon = ((dvar1 ^ 2 / dcnt1) ^ 2 / (dcnt1 - 1)) + ((dvar2 ^ 2 / dcnt2) ^ 2 / (dcnt2 - 1))
	dResult = dNumer / dDenon
Else
	dResult = dcnt1 + dcnt2 - 2
End If
 
DOFTTESTM = dResult
 
Exit Function
 
DOFTTESTM_Error:
	DOFTTESTM = Null
 
End Function

Convert Text to Uppercase

admin — Mon, 17 Sep 2007 13:21:00 +0000

If you want to convert the text to uppercase, use the following code; however, I recommend downloading ASAP Utilities, it has many functionalities, including text conversion. It doesn’t offer source code though.

Here’s my code for uppercase conversion:
(If you want to convert your text to lowercase, replace Ucase with Lcase function in the code)

‘Will convert selected range to Upper case, using array
Sub Conv2UCase()
On Error GoTo Conv2UCase_Error

Dim vDataArr As Variant
Dim lUpperBndRow As Long, lUpperBndCol As Long
Dim lRow As Long, lCol As Long

‘store selected values in an array
vDataArr = Selection
‘get the upper bound of rows
lUpperBndRow = UBound(vDataArr, 1)
‘get the upper bound of cols
lUpperBndCol = UBound(vDataArr, 2)

‘Start a loop to go through all the elements of the array
For lRow = 1 To lUpperBndRow
    For lCol = 1 To lUpperBndCol
        ‘Check if the value is text, if not don’t convert
        If WorksheetFunction.IsText(vDataArr(lRow, lCol)) Then
            ‘Convert values to upper case
            vDataArr(lRow, lCol) = UCase(vDataArr(lRow, lCol))
        End If
    Next lCol
Next lRow
‘Return the converted values to the range
Selection = vDataArr
Exit Sub

Conv2UCase_Error:
MsgBox “Error ” & Err.Number & ” (” & Err.Description & “) in Sub:Conv2UCase”
End Sub

A function to reverse a string

admin — Thu, 16 Aug 2007 14:19:00 +0000

Very simple, uses the VBA function StrReverse to reverse the input string.

‘A function to reverse a string provided as input
‘For example, the string “abcd” will become “dcba”
‘Uses the VBA function StrReverse
Public Function ReverseString(sInputString As String) As String
On Error GoTo ReverseString_Error

ReverseString = StrReverse(sInputString)
Exit Function

ReverseString_Error:
ReverseString = “#ERROR#”
End Function

Concatenate function

admin — Tue, 24 Jul 2007 16:24:00 +0000

Oh, man, I can’t tell how useful that concatenate function is.

One repetitive use I found is to create OR/AND conditions for Access queries. I copy-paste the field values of a column from Access, do some filtering and my conditions are ready. Then I use this concatfunc to create a string to use in my Access query.

For example, look at this print screen:

The Range A1:A4 houses the string condition I want to use in my Access query to restrict the fruits from my data. In cell B1 I have the formula

=PERSONAL.XLS!concatfunc(A1:A4,CHAR(34) & ” or ” & CHAR(34))

, and the return string from this function is listed in cell B1.

Now, all you have to do is copy and paste this in Access criteria and put a quotation mark at the start and at the end of this string.

I have found one more use of this when I want to store some values in an Array, using the Array function in VBA.

One more print screen:

In this example, I insert a comma (CHAR(44) instead of string OR, and this function returns a string that I can use in VBA to store these values in an array using Array function, after adding a quotation mark, of course, at the start and at the end.

Range Concatenation with a character

admin — Fri, 29 Jun 2007 14:03:00 +0000

Are you frustrated that you have to concatenate a range, and you have to do that using CONCATENATE formula by entering each cell and typing a comma after every cell? Well, here’s a solution to it. A procedure or a function whatever you like. If you use the procedure, it allows you to choose the input range, concatenate character, and the output range. If you use the function, then you can enter the optional concatenate character (by default it is a comma (,)), and the input range.

Here are both:

Procedure:

Public Sub ConCatwChar()
Dim sChar2bAdded As String, rngRng2bCated As Range, sOutput As String, rngTarget As Range, c As Range
On Error GoTo ConCatwChar_Error
‘You could use this line to return the concatenated string in this cell
‘Set rngTarget = ActiveCell

Set rngRng2bCated = Application.InputBox(prompt:=”Select the range you’d like to concatenate with a charcter”, _
Title:=”Select Range”, Type:=8)

If rngRng2bCated Is Nothing Then Exit Sub

‘You could use this line to set the default to a comma and remove the inputbox line
‘sChar2bAdded = “,”
sChar2bAdded = InputBox(“Enter the character you’d like to add between other cells”, “Enter Character”, “,”)

Set rngTarget = Application.InputBox(prompt:=”Select the range you’d like the output”, _
Title:=”Select Range”, Type:=8)

For Each c In rngRng2bCated
sOutput = sOutput & c.Value & sChar2bAdded
Next c

sOutput = Left(sOutput, Len(sOutput) – Len(sChar2bAdded))
rngTarget = sOutput

On Error GoTo 0
Exit Sub

ConCatwChar_Error:
MsgBox “Error ” & Err.Number & ” (” & Err.Description & “) in procedure ConCatwChar”
End Sub

Here’s the function:

‘You can change the option string character to nothing “” so that you get concatenated string without a character in between
Public Function ConCatFunc(rngRng2bCated As Range, Optional sChar2bAdded As String = “,”) As String
Dim sOutput As String, c As Range

On Error GoTo ConCatFunc_Error

For Each c In rngRng2bCated
sOutput = sOutput & c.Value & sChar2bAdded
Next c
sOutput = Left(sOutput, Len(sOutput) – Len(sChar2bAdded))
ConCatFunc = sOutput

On Error GoTo 0
Exit Function

ConCatFunc_Error:
ConCatFunc = “#Error#”

End Function

Isworksheetopen and Isworkbookopen functions

admin — Wed, 23 Feb 2005 05:14:00 +0000

Here’s a IsWorkbookOpen function to check if a workbook is open or not. Returns TRUE or FALSE

Public Function IsWorkbookOpen(ByVal wkbkname As String) As Boolean

Dim Wb As Workbook
‘check if its already opened in the Windows collection
For Each Wb In Workbooks
If Wb.Name = wkbkname Then IsWorkbookOpen = True
GoTo exitsub

End If
Next Wb

exitsub:
End Sub

Here’s a IsWorksheetOpen function to check if a worksheet is open or not. Returns TRUE or FALSE

Public Function IsWorksheetOpen(ByVal wsname As String) As Boolean
Dim wk As Worksheet
For Each wk In Worksheets
If wk.Name = wsname Then
IsWorksheetOpen = True
GoTo exitsub
End If
Next wk
exitsub:
End Function

Excel Function to check if text is palindrome or not

admin — Thu, 10 Feb 2005 15:16:00 +0000

Definition of palindrome as given in Answers.com

pal?in?drome (p?l’?n-dr?m’)

A word, phrase, verse, or sentence that reads the same backward or forward. For example: A man, a plan, a canal, Panama!

Function IsPalindrome(sInput As String) As Boolean
If sInput = StrReverse(sInput) Then
IsPalindrome = True
Else
IsPalindrome = False
End If
End Function