MA3696 Lecture 6

LECTURE 6

2D Arrays
Algorithms

SUMMARY
Quick recap of 1D arrays
2D Arrays
 Declaring and re-declaring
 Assigning values
 Outputting values

Algorithms
 Mapping out the tasks needed for a program

REVIEW OF 1D ARRAYS

Const NSTOCKS as Integer = 2
ReDim meanRet(NSTOCKS) as Double
Const TIMEPERIODS as Integer = 4
Dim stockReturns(TIMEPERIODS) as Double
**Assume we’re using Option Base 1**

REVIEW OF 1D ARRAYS

stockReturns(2) = ? _


REVIEW OF 1D ARRAYS

stockReturns(2) = 0.0024


REVIEW OF 1D ARRAYS

stockReturns(4) = ? _


REVIEW OF 1D ARRAYS

stockReturns(4) = 0.0052


REVIEW OF 1D ARRAYS

meanRet (1) = ? _


REVIEW OF 1D ARRAYS

meanRet (1) = 0.00371


ARRAYS
Hold a range (or set) of values
Basically a set of variables
Your arrays will mainly be 1 or 2 dimensions

arrayName(5)

arrayName(5)

arrayName(5, 4)

arrayName is the name of your array

ARRAYS
Hold a range (or set)about 2D Arrays
of values
Today is
Basically a set of variables
Your arrays will mainly be 1 or 2 dimensions

arrayName(5)

arrayName(5)

arrayName(5, 4)

arrayName is the name of your array

DECLARING ARRAYS
The same rules apply to 2D arrays as to 1D arrays
 Disposable, local or global? – Declare in the right place
 Must specify a data type

Public Sub DescriptiveStats()
Dim stockPrices(5, 2) As Double
Dim stockRet(4, 2) As Double
End Sub

These are
disposable

DECLARING ARRAYS
The same rules apply to 2D arrays as to 1D arrays

Also, need to specify the size of the array
 The “size” is the number of elements in the array

End Sub

5 rows
2 columns
4 rows
2 columns

DECLARING ARRAYS returns
5 stock prices
4 stock
2 rules
2 variables
The same stocks apply to arrays as to stocks

Also, need to specify the size of the array
 The “size” is the number of elements in the array

End Sub

5 prices
2 stocks
4 returns
2 stocks

DECLARING ARRAYS (1D

AND

2D)

Many times we don’t know the number of
elements that will be in the array.
So, first declare them empty, like this:
Dim stockPrices() As Double
Dim stockRet() As Double

For example,
these are local

End Sub

General format
for declaration

arrayName() As DataType
arrayName:= the name of the array
DataType:= Integer, Double, String…

DECLARING ARRAYS
After the size of the array is know, re-declare it
inside a procedure
Dim stockPrices() As Double, stockRet() As Double
Dim nDays As Integer, nStocks As Integer

Arrays will most likely need
to be local or global
These are local

DECLARING ARRAYS
inside a procedure
nDays = ComboBox1.Value
nStocks = ComboBox2.Value

End Sub

User selects number
of days from a
ComboBox on the
userform

DECLARING ARRAYS
inside a procedure

End Sub

User selects number
of stocks from a
ComboBox on the
userform

DECLARING ARRAYS
inside a procedure

Redim both arrays
using the variables

Redim stockPrices(nDays, nStocks) As Double
Redim stockRet(nDays-1, nStocks) As Double
End Sub

DECLARING ARRAYS
inside a procedure
Num Rows
Num Cols
Redim stockPrices(nDays, nStocks) As Double
Redim stockRet(nDays-1, nStocks) As Double
End Sub

DECLARING ARRAYS
inside a procedure

General format for
re-declaration

ReDim arrayName(nRows, nCols) As DataType
nRows:= the number of rows in the array
nCols:= the number of columns in the array

SUMMARY OF DECLARING 2D ARRAYS
If the size of the array is known and constant
 Declare the constants for nRows and nCols as global

 Declare the arrays (disposable, local or global) using the
constants as the nRows and nCols

Public Const TIMEPERIODS As Integer = 5
Public Const NSTOCKS As Integer = 2
Dim stockPrices(TIMEPERIODS, NSTOCKS) As Double
Dim stockRet(TIMEPERIODS-1, NSTOCKS) As Double
Remember to use Public instead of Dim if they are global.

If the size of the array is unknown or variable
 Declare the arrays empty (disposable, local or global)


 Declare variables for nRows and nCols (disposable, local or
global) and assign them values


 Declare variables for nRows and nCols (disposable, local or
global) and assign them values
 Redim the arrays using the variables

2D ARRAYS
VBA counts elements of 1D and 2D arrays from 0
For example,
 This array is named stockPrices
 It has 5 rows and 2 columns: stockPrices(5, 2)

Count
0
1
2
3
4

0

1

stockPrices(0, 0)

2D ARRAYS
VBA counts elements of 1D and 2D arrays from 0
For example,
 This array is named stockPrices
 It has 5 rows and 2 columns: stockPrices(5, 2)

Count
0
1
2
3
4

0

1

stockPrices(4, 1)

2D ARRAYS
To force VBA to count from 1
 Use Option Base 1 at the top of each module

Count
1
2
3
4
5

1

2

stockPrices(1, 1)

2D ARRAYS
To force VBA to count from 1
 Use Option Base 1 at the top of each module

Count
1
2
3
4
5

1

2

stockPrices(5, 2)

EXERCISE 1. DECLARING 2D ARRAYS
Use Lecture 6 Student Example.xlsm, Module1
Declare an array to store the stock returns shown:
 The array can be declared as disposable, local or global.
 Assume you know in advance that:
 nRows is the constant TIMEPERIODS
 nCols is the constant NSTOCKS

EXERCISE 2. DECLARING 2D ARRAYS
Use Lecture 6 Student Example.xlsm, Module1
Declare an array to store the stock returns shown:
 The array can be declared as disposable, local or global.
 Assume that nRows and nCols are NOT known in advance:
 nRows is the variable nTimePeriods. Assign a value in the procedure
 nCols is the variable nStocks. Assign a value in the procedure

‘FILLING’ ARRAYS
USING NAMED RANGES

FILLING 1D ARRAYS FROM A NAMED RANGE

Range(“StockPrices”).Cells(1, 1)


Range(“StockPrices”).Cells(10,1)


For i = 1 to TIMPERIODS
stockPrices(i) = Range(“StockPrices”).Cells(i,1)
Next i


For k = 1 to NSTOCKS
For i = 1 to TIMPERIODS
stockPrices(i,k) = Range(“StockPrices”).Cells(i,k)
Next i
Next k

OUTPUTTING ARRAYS
USING NAMED RANGES

OUTPUTTING 1D ARRAY TO A NAMED RANGE

Range(“StockReturns”).Cells(1, 1)

Range(“StockReturns”).Cells(9,1)


For i = 1 to TIMPERIODS - 1
Range(“StockReturns”).Cells(i,1) = stockReturns(i)
Next i

EXERCISE 3. FILL AND OUTPUT
 Use Lecture 6 Student Example.xlsm, Module1
 Read in the prices from the range “PricesPence” to
an array with the same name
Convert the pence to pounds and assign the values
to an array called PricesPounds()
 Output the values of PricesPounds() to the named
range “PricesPounds”
REMEMBER: Generalise your code!
Ranges have been named.

THINK ABOUT THE PROCESS
 Taking a road trip
 Just get in the car and drive, OR
 Make a plan and print directions (or set the sat nav)?

When you write a program
 Go straight to VBA and try typing some code? NO!
 Make a plan first!

Why is this so difficult?
 The plan is usually written for you (assignments, labs,
etc…). You just have to follow the steps already given.
 When you write a program/software, there are no steps
given – you have to write them.

TASK ANALYSIS

(JOHNSON, 2010)

(A few) questions you should answer first:
 What will the user want to achieve with this software?
 Portfolio optimisation, simulation, risk analysis, etc…?

 What tasks are needed in order to get the end result?
 Select stocks, assign weights, choose capital to invest, etc…?

 What are the steps for each task?
 Will they select stocks from a list, will they enter weights or
investments, navigate with command buttons, etc…?

 What tools are used to complete the steps for each task?
 Includes userform controls as well as programing tools?

 Where does the information for each task come from?
 Are stock prices already in the spread sheet or downloaded from
the internet, what information is entered by the user, etc…?

TASK ANALYSIS (CONT’D) ( J O H N S O N , 2 0 1 0 )
 What is the result/output of each task?
 How will the result of each task be used?
 Count how many stocks are chosen, output chosen stocks on a
separate sheet, etc…?

 What problems may users have in doing these tasks?
 Will they know what order to do things & understand instructions?

 What are common user mistakes?
 Entering decimal numbers instead of integers, trying to move
forward without completing all steps, etc…?

 How will you deal with these errors when they occur?
 What terminology will the user be familiar with?
 Can they understand your lingo?

BREAKING DOWN A COMPLICATED TASK
You cannot write a complicated program without
planning.

Break everything down into simple steps
You will never write a ‘perfect’ program without
first making mistakes
 Trial and error – that’s part of programming
 Just because it doesn’t work the first time, don’t give up
 If something isn’t ‘working’ it’s probably an error on your
part, not VBA.

The hardest part of creating a program is writing
out the process. Usually, the actual code is fairly
straight forward.

EXAMPLE. BREAKING DOWN TASKS
Task 1: Select a time period
Task 2: Enter investments
Task 3: Click ‘Estimate
return’ button
Task 4: Review investment
on next userform.
Task 5: Click ‘Change
investment’ button
Task 6: Click ‘Quit’ button

EXAMPLE. TASK 1 – SELECT TIME
 User selects time from combobox
 Fill combobox BEFORE user sees
 Userform initialise: add items

 When the user selects a time:
 Name the range of prices
corresponding to that time
 Use that range to calculate stats
 I’ll need the means later, so assign those to
an array first
 Then use the array of means to assign
values to the labels.

 Display those stats on the userform
 Format the display to be %
 Enable the textboxes

EXAMPLE. TASK 2 - INVESTMENTS
 The user enters investments in
the textboxes.

EXAMPLE. TASK 3 – CLICK BUTTON
 Check user entries:
 Check for letters, blanks & negative
numbers

 I’ll need to use investments in a
calculation so assign them to an
array.
 Calculate total investment
 Add together all investments

 Calculate the final value
 Need means and investments

 Calculate the return
 (final value/total investment)–1

 Show the next userform

EXAMPLE. TASK 4 – REVIEW RESULTS
 Output should display BEFORE the
user sees the form (initialise sub)
 Display total investment (£)
 Assign the label the value of the total
investment variable
 Format label as £0.00

 Display portfolio return
 Assign the label the value of the portfolio
return variable
 Format label as 0.000%

 Display final investment value (£)
 Assign the label the value of the final
investment variable
 Format label as £0.00

EXAMPLE. TASK 5 – CHANGE INVESTMENT
 User wants to change their
investments:
 Unload the investment summary
userform

EXAMPLE. TASK 6 – QUIT
 User wants to quit the program:
 Ask user if they are sure they want to
quit as this will close the program
 If yes, then unload both userforms
 If no, then do nothing

LEARNING OUTCOMES
You are ready to move on when…
 LO26: You can declare a 2D array with the correct number
of elements, in the correct location within your code and
with the correct data type. In addition, you understand
when to declare an array empty and how to use the ReDim
statement.
 LO27: You can assign values to a 2D array as well as assign
the values of a 2D array to cells, a range or userform
controls.
 LO28: You can list the questions we should ask when
developing a program. You can describe what is meant by
a ‘task’ as part of a program. Lastly, you can identify the
tasks of a program in order to construct an algorithm.

MA3696 Lecture 6

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MA3696 Lecture 6