ACC1x: How To Compute Moving Averages in Access Basic (1.x)
ID: Q106245
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The information in this article applies to:
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Microsoft Access versions 1.0, 1.1
SUMMARY
Advanced: Requires expert coding, interoperability, and multiuser skills.
The following sample Access Basic function computes a moving average for a
set of values in a table based on a given period of time. For example, if
you have data that has been collected weekly for the past year, and you
want to compute a historical average for a three-week time period on each
value, you can use this function to return an average for each value in the
table based on the current value and the values from the two previous
weeks.
MORE INFORMATION
This article assumes that you are familiar with Access Basic and with
creating Microsoft Access applications using the programming tools provided
with Microsoft Access. For more information on Access Basic, please refer
to the "Introduction to Programming" manual in Microsoft Access version
1.x.
The sample function below computes moving averages based on a table with a
multiple-field primary key. The weekly values of foreign currencies are
used for this example.
- Create the following table. Save the table as Table 1.
Table: Table 1
-----------------------------------------
Field Name: CurrencyType [Primary Key]
Data Type: Text
Field Size: 25
Field Name: TransactionDate [Primary Key]
Data Type: Date/Time
Format: Short Date
Field Name: Rate
Data Type: Currency
Decimal Places: 4
- View the table in Datasheet view, and type the following values:
CurrencyType TransactionDate Rate
--------------------------------------------
Yen 8/6/93 $0.0079
Yen 8/13/93 $0.0082
Yen 8/20/93 $0.0085
Yen 8/27/93 $0.0088
Yen 9/3/93 $0.0091
Mark 8/6/93 $0.5600
Mark 8/13/93 $0.5700
Mark 8/20/93 $0.5800
Mark 8/27/93 $0.5900
Mark 9/3/93 $0.6000
- Open a new module and type the following functions:
'*************************************************************
'Declarations section of the module.
'*************************************************************
Option Explicit
'===============================================================
' The following function MAvgs computes moving averages based on
' a table with a multiple field primary key.
'===============================================================
Function MAvgs(Periods As Integer, StartDate, TypeName)
Dim MyDB As DATABASE, MyTable As TABLE, MySum As Double
Dim i, x
Set MyDB = CurrentDb()
Set MyTable = MyDB.OpenTable("Table 1")
On Error Resume Next
MyTable.Index = "PrimaryKey"
x = Periods - 1
ReDim Store(x)
MySum = 0
For i = 0 To x
MyTable.MoveFirst
MyTable.Seek "=", TypeName, StartDate
' These two variables should be in the same order as the
' primary key fields in your table.
Store(i) = MyTable![Rate]
If i <> x Then StartDate = StartDate - 7
'7 here assumes weekly data; you would use 1 for daily
' data.
If StartDate < #8/6/93# Then MAvgs = Null: Exit Function
'#8/6/93# is replaced with the earliest date of the data
' in your table.
MySum = Store(i) + MySum
Next i
MAvgs = MySum / Periods
MyTable.Close
End Function
- Create the following query based on Table 1:
Query: Query1
------------------------------------------------------
Field: CurrencyType
Field: TransactionDate
Field: Rate
Field: Expr1: MAvgs(3,[TransactionDate],[CurrencyType])
NOTE: This query will generate a 3-week moving average of the Rate data.
To compute a longer or shorter moving average, change the "3" in the
query's Expr1 column to the value you want to compute.
- Run the query.
You will see a 3-week moving average for each currency. A null indicates
that there were not enough prior values to compute that week's average.
NOTE: If you want to compute a moving average for a table with a single
primary key, use the primary key both as an argument to be passed to the
function and as the key value for the Seek method.
Additional query words:
rolling
Keywords : kbprg
Version : WINDOWS:1.0,1.1
Platform : WINDOWS
Issue type : kbhowto