MA3696 Lecture 6

2D Arrays

Algorithms LECTURE 6

Quick recap of 1D arrays

2D Arrays

Declaring and re-declaring

Assigning values

Outputting values

Algorithms

Mapping out the tasks needed for a program

SUMMARY

Const TIMEPERIODS as Integer = 4 Dim stockReturns(TIMEPERIODS) as Double

Const NSTOCKS as Integer = 2 ReDim meanRet(NSTOCKS) as Double

REVIEW OF 1D ARRAYS

**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


2D ARRAYS

Hold a range (or set) of values

Basically a set of variables

Your arrays will mainly be 1 or 2 dimensions

arrayName is the name of your array

ARRAYS

arrayName(5) arrayName(5) arrayName(5, 4)

arrayName(5) arrayName(5)

Hold a range (or set) of values

Basically a set of variables

Your arrays will mainly be 1 or 2 dimensions

arrayName is the name of your array

ARRAYS

Today is about 2D Arrays

arrayName(5, 4)

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

DECLARING ARRAYS

Public Sub DescriptiveStats()

Dim stockPrices(5, 2) As Double

Dim stockRet(4, 2) As Double

End Sub

These are disposable

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

DECLARING ARRAYS




End Sub

5 rows 2 columns

4 rows 2 columns

The same rules apply to arrays as to variables



Also, need to specify the size of the array

The “size” is the number of elements in the array

DECLARING ARRAYS 5 stock prices 2 stocks

4 stock returns 2 stocks




End Sub

5 prices 2 stocks

4 returns 2 stocks

Many times we don’t know the number of elements that will be in the array.

So, first declare them empty, like this:

DECLARING ARRAYS (1D AND 2D)

Dim stockPrices() As Double Dim stockRet() As Double


End Sub

arrayName() As DataType

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

General format for declaration

For example, these are local

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

DECLARING ARRAYS

Arrays will most likely need to be local or global

These are local




nDays = ComboBox1.Value nStocks = ComboBox2.Value

End Sub

DECLARING ARRAYS

User selects number of days from a

ComboBox on the userform





End Sub

DECLARING ARRAYS

User selects number of stocks from a

ComboBox on the userform





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

End Sub

DECLARING ARRAYS

Redim both arrays using the variables





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

End Sub

DECLARING ARRAYS

Num Rows Num Cols


DECLARING ARRAYS

ReDim arrayName(nRows, nCols) As DataType

nRows:= the number of rows in the array nCols:= the number of columns in the array

General format for re-declaration

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

SUMMARY OF DECLARING 2D ARRAYS

Public Const TIMEPERIODS As Integer = 5Public Const NSTOCKS As Integer = 2

Dim stockPrices(TIMEPERIODS, NSTOCKS) As DoubleDim 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


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)

2D ARRAYS

stockPrices(0, 0)

Count

0 1 2 3 4

0 1

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)

2D ARRAYS

stockPrices(4, 1)

Count

0 1 2 3 4

0 1

To force VBA to count from 1

Use Option Base 1 at the top of each module

2D ARRAYS

stockPrices(1, 1)

Count

1 2 3 4 5

1 2

To force VBA to count from 1

Use Option Base 1 at the top of each module

2D ARRAYS

stockPrices(5, 2)

Count

1 2 3 4 5

1 2

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 1. DECLARING 2D ARRAYS


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

EXERCISE 2. DECLARING 2D ARRAYS

‘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 TIMPERIODSstockPrices(i) = Range(“StockPrices”).Cells(i,1)

Next i












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

Next i













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.

EXERCISE 3. FILL AND OUTPUT

ALGORITHMS

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.

THINK ABOUT THE PROCESS

(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 ( 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?

TASK ANALYSIS (CONT’D) ( J O H N S O N , 2 0 1 0 )

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.

BREAKING DOWN A COMPLICATED TASK

EXAMPLE ALGORITHM

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. BREAKING DOWN TASKS

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 1 – SELECT TIME

The user enters investments in the textboxes.

EXAMPLE. TASK 2 - INVESTMENTS

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 3 – CLICK BUTTON

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 4 – REVIEW RESULTS

User wants to change their investments: Unload the investment summary

userform

EXAMPLE. TASK 5 – CHANGE INVESTMENT

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

EXAMPLE. TASK 6 – QUIT

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.

LEARNING OUTCOMES

THE END

MA3696 Lecture 6

Education

double dim ndays

double dim stockret4

d arrays disposable

d arrays of values

double dim stockrettimeperiods

d arrays algorithms

d arraysconst nstocks

dim stockpricestimeperiods