Ch9 - CP212
Slides updated Feb 6, 2013
A Product Mix Application
• brief look at a complex application
• Chapter 21 - Product Mix.xlsm
•
•
o Chapter 20 deals with a Blending Application - VBA is
simpler (most done ahead of time, lots of charts)
uses linear programming
Illustrates custom made wood furniture
Resources
• Labour Hours for Senior Woodworkers
• Labour Hours for Junior Wood Workers
• Machine Hours
• Wood (measured in board feet)
o Oak
o Cherry
Different products can be made from each
type of wood:
End tables, Rocking chairs, Coffee tables, Desks,
Bookshelves
•
Constraints
• Each product has a constraint on MAX/MIN production levels
Objective
• Maximize profit: revenues - costs
Open Product Mix.xlsm
Arrays
• basic data structure used to organize lists
• known as Lists in Python but with limited operations
• each element is accessed by its index
• index can be base 0 or base 1, base 0 is default.
• Base 1 may seem more natural, but it is uncommon in
programming
• Visual Basic .Net does not have the option for Base 1, so if
you are moving up, don't get used to it.
Arrays - Like Mailboxes, but different
• used to store values of the same data
•
type (here, String)
referenced by index number
Sub ArraysChapter9()
' Declare an array of 6 pets
Dim pets(5) As String
Dim pet As Variant
pets(0) = "Cat"
pets(1) = "Dog"
pets(2) = "Fish"
pets(3) = "Snake"
pets(4) = "Lemur"
pets(5) = "Meerkat"
' Loop through the array, though can't extract the index number.
For Each pet In pets
MsgBox "The pet is a " & pet
Next
End Sub
Sales Regions Example
See Transactions Finished.xlsm
Dim myArray(n) As dataType
Declares an array with n+1 elements.
Using Base 0 arrays:
Dim scores(99) gives us 100 elements
Dim scores(100) gives us 101 elements
Sub Sample()
Dim scores(100) As Byte
scores(100) = 5 ' Legal
MsgBox "scores(100) = " & scores(100)
scores(101) = 5 ' Illegal
End Sub
More arrays
• can specify arrays with the values
•
o Dim scores() As Variant
o scores = Array("4", "5", "6", "7", "2")
or
o Dim daysOfTheWeek() As Variant
o daysOfTheWeek = Array("Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun")
• need to use Variant in this case
Rules with Arrays
• different ways of declaring arrays
o Dim pets(0 to 5) As String
• dynamic arrays
o Dim pets() As String ' No size yet
o Can resize with ReDim
 Redim pets(newSize) ' or Redim pets(0 to newSize)
o redim will delete the existing values in the array
Rules of Arrays (cont'd)
• Dynamic arrays can be resized at runtime
•
o need to preserve the values during resize?
 ReDim Preserve pets(newSize) or
 ReDim Preserve pets(0 to newSize)
Cannot resize static arrays
o Dim pets(5) As String
 ReDim Preserve pets(6) will give an error message
 can't redim arrays that have fixed size at compile time
Board Code
Sub staticArraysExample()
Dim cars(3) As String
cars(0) = "Lynx"
cars(1) = "Tiger"
cars(2) = "Wombat"
cars(3) = "Ptarmigan"
' cars(4) = "Ermine" ' FAIL!
' ReDim Preserve cars(5) ' FAIL!
End Sub
Sub dynamicArraysExample()
Dim animals() As String
Dim msg As String
Dim i As Byte
' Resize the array at runtime
ReDim animals(3)
animals(0) = "Lynx"
animals(1) = "Tiger"
animals(2) = "Wombat"
animals(3) = "Ptarmigan"
'animals(4) = "Stoat" ' FAIL!
' Resize to add more.
ReDim Preserve animals(5)
animals(4) = "Stoat"
animals(5) = "Dragon"
For i = 0 To 5
msg = msg & animals(i) & vbCrLf
Next i
MsgBox "The animals are now: " & vbCrLf & msg, vbInformation, "Dynamic Array Resized"
End Sub
• LBound, UBound (UBound on page 194)
• Join And Split (not in text)
• See Chapter9Example files regarding LBound, UBound and
Join & Split
• Multidimensional arrays (page 158)
Looking Up a Price
• could easily be done with vlookup() - recommend you learn it
• See Unit Prices.xlsm
1.Find the number of items
2.redim the arrays to the proper size
3.Loop through column A (in an array), and as a new product
is found, store it in an array called productCodes and
increase the number of unique productCodes
4.Do the same for unitPrices
5.Find the product in the product array and display its unit
price
Code Highlights
Travelling Sales Person
• a common algorithm used in computer science
• a basic solution is called the "nearest-neighbour heuristic"
• play with the spreadsheet, run it a few times
• examine the code
• nothing new, but the algorithm may be complex
• simple to understand, difficult to code
Merging Lists
• two lists: last year's customers and this year's customers
• want to make one list of customers from both years
o no duplicates
o merge, not append
• think of a manual solution first
o its the only way you can code one
o write it out (pseudocode, comments)
Merging (cont'd)
1.Start at the top of each list and compare names
o if they are the same, put the name in column D
 then move to the next item in both columns
o if name in col A comes before name in col B, put it in col D
and move down to the next item in col A (but not B)
 similar if name in B comes before name in A
2.Continue until all names from one column have been
transferred
o then just copy over the rest of the names in the remaining
column
Now, can you code it?
Merging - Useful Code
Fill a Range from an Array (Array Fill)
•
much quicker than looping
Dim adblTempArray() As Double
Dim rngTheRange As Range
' Array gets filled with lots of values
' Range is defined to be same size as # of values in array
' (or less)
' Place all values in the array in each cell in the range
rngTheRange.Value = adblTempArray
(see loop fill vs. array fill.xlsm in MyLS)
Fill a Range from an Array - Transpose
The ‘shape’ (horizontal or vertical) of an array and the range it
is copied to must match.
Dim values (1 To 10) As Integer
… fill array
Range(“A1:J1”) = values
Works as expected. To put this horizontal array into a vertical
column requires transposing the values:
Range(“A1:A10”) = Application.Transpose(values)
Fill Array from a Range
Dim values(10) As Integer
values = Range(“A1:J1”)
defines a row spanning 10 columns.
Dim values(10,0) As Integer
values = Range(“A1:A10”)
defines a column spanning 10 rows
Because it is 2D, items are accessed with:
For i = 1 To 10
values(i,0)