Ch9 - CP212

Slides updated Feb 6, 2013

A Product Mix Application

•brief look at a complex application•Chapter 21 - Product Mix.xlsmoChapter 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)oOakoCherry

 Different products can be made from eachtype 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 petsDim pets(5) As StringDim 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 " & petNextEnd 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 elementsDim 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 ' IllegalEnd Sub

More arrays

•can specify arrays with the valuesoDim scores() As Variantoscores = Array("4", "5", "6", "7", "2")

•oroDim daysOfTheWeek() As VariantodaysOfTheWeek = Array("Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun")

•need to use Variant in this case

Rules with Arrays

•different ways of declaring arraysoDim pets(0 to 5) As String

•dynamic arraysoDim pets() As String ' No size yetoCan resize with ReDim

Redim pets(newSize) ' or Redim pets(0 to newSize)oredim will delete the existing values in the array

Rules of Arrays (cont'd)

•Dynamic arrays can be resized at runtimeoneed to preserve the values during resize?

ReDim Preserve pets(newSize) or  ReDim Preserve pets(0 to newSize)

•Cannot resize static arrayso 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 items2.redim the arrays to the proper size3.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 unitPrices5.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 yearsono duplicatesomerge, not append

•think of a manual solution firstoits the only way you can code oneowrite it out (pseudocode, comments)

Merging (cont'd)

1.Start at the top of each list and compare namesoif they are the same, put the name in column D

then move to the next item in both columnsoif 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 transferredothen 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 DoubleDim 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 rangerngTheRange.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 arrayRange(“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 Integervalues = Range(“A1:J1”)

defines a row spanning 10 columns.

Dim values(10,0) As Integervalues = Range(“A1:A10”)

defines a column spanning 10 rowsBecause it is 2D, items are accessed with:

For i = 1 To 10values(i,0)