GENG2140 Lecture 4: Introduc4on to Excel spreadsheets. A/Prof Bruce Gardiner School of Computer Science and SoDware Engineering 2012

Transcription

1 GENG2140 Lecture 4: Introduc4on to Excel spreadsheets A/Prof Bruce Gardiner School of Computer Science and SoDware Engineering 2012 Credits: Nick Spadaccini, Chris Thorne

2 Introduc4on to spreadsheets Used as an electronic list Used as a more convenient calculator Used as a quick plolng and data presenta4on tool Used for data manipula4on and includes a number of programming tools

3 Why use spreadsheets? powerful, simple to use and it is possible to execute rapid analysis summarises raw data and produces informa4on results presented in a variety of forms performs analysis and improves planning and modelling has a range of in- built func4ons can apply analy4cal op4mizing tools can build and simulate different models using scenario planning

4 Excel for data presenta4on

5 Introduc4on to spreadsheets Contain a number of cells which can be iden4fied or referred to by their posi4on Specifically a cell can be iden4fied by the row and column in which it appears. In excel, columns (ver4cal) have been assigned a le[er and rows (horizontal) a number 1 A B C D E F E3

6 Cell referencing Rela4ve references are just column and row labels, eg. B3. The cell addressed is rela4ve to the current ac4ve cell. 1 C A B C D E F 2 +B B1 C2 has the value in the cell 1 rows up and 1 column to the left If the rela4ve reference in C2 was copied and pasted to D4. D4 would take the value of cell C3

7 Cell referencing Absolute references prefix column and row labels with $, eg. $B$1. The cell addressed is a specific cell 1 C A B C D E F 2 +$B$ $B$1 C2 has the value in cell B1 If the absolute reference in C2 was copied and pasted to D4. D4 would take the value of cell B1

8 Cell referencing Mixed references prefix either a column or row labels with $, eg. $B1 or B$1. 1 C A B C D E F 2 +$B $B1 C2 has the value in column B, 1 row up from the active cell If the absolute reference in C2 was copied and pasted to D4. D4 would take the value of cell B3

9 Cell referencing Mixed references prefix either a column or row labels with $, eg. $B1 or B$1. 1 C A B C D E F 2 +B$ B$1 C2 has the value in Row 1 1 column to left of the active cell If the absolute reference in C2 was copied and pasted to D4. D4 would take the value of cell C1

10 Cell referencing between worksheets You can reference ALL cells in the workbook. This includes values in cells on other worksheets. Precede any cell reference with the worksheet name (which is always an absolute reference), e.g. Sheet1!B3. The! is a separator and its right hand side can be any reference type.

11 Cell referencing - ranges Ranges of cells use the : separator eg. B3:D4. All cells between and including the two reference cells (B3 and D4) are included in the range ie. a 2x3 block of cells.

12 Formulae Calcula4ons can performed within a cell, using formulas which may reference other cells Formulas within cells A B 1 2 +$a$1*a2 2 +a Values displayed in cells A B

13 Formulae Copying and pas4ng formulas to new cells automa4cally changes the formula according to the referencing (rela4ve, absolute, mixed) Formulas within cells A B 1 2 +$a$1*a2 2 +a1+2 +$a$1*a3 3 +a2+2 +$a$1*a4 4 +a3+2 Values displayed in cells A B

14 Func4ons Excel provides hundreds of worksheet func0ons for use within formulae. A func0on is a pre- defined set of instruc4ons that you execute by making a func0on call like this, Name of the func/on Parentheses (required) =Func/onName(Arguments) The data the func/on operates over. Place the result of this func/on in this currently ac/ve cell Cell, range of cells or data We take a black box approach to functions. We provide the input arguments in the form it requires, it returns the result of the operations over that data.

15 Finding Func4ons Inbuilt func4ons can be found in the Formulas menu. Some4mes you can get lucky and start typing the likely func4on name in the cell e.g. +Average(.. and excel will suggest the func4on you want We take a black box approach to functions. We provide the input arguments in the form it requires, it returns the result of the operations over that data.

16 Func4ons Example : Average Name of the func/on Parentheses (required) =AVERAGE(number 1, number 2, ) Place the result of this func/on in this currently ac/ve cell Cell, range of cells or data +AVERAGE(c1:c15) Would give the average of all the values in the cells c1 through to c15

17 Func4on example - IF Used to embed logic within a worksheet Rela4onal and Logical operators can be used in a condi4on =IF(Q1>=0,(- B1+SQRT(Q1))/2*A1, Root is Imaginary ) arg 1 arg 2 arg 3 The IF func4on has 3 arguments, (arg 1) a test which results in TRUE or FALSE, (arg 2) the instruc4ons to execute if the test is TRUE. (arg 3) else the instruc4ons to execute if the test is FALSE. Text and numbers can be used in an IF func4on Text must be enclosed within double quota4on marks Numbers appear without quota4on marks

18 Naming cell references Cells and cell ranges can be referenced by name. +Average(Exam_grade) +Coun0f(Exam_grade, >=7.5 ) ADVANTAGES: easier to read and understand the formulae, compare +Average(Exam_grade) =Average(a1:a9) you can update the reference in one place (including cell range) and everything automa4cally updates.

19 A mul4- cell array formula The product of two cells is given by =A1*B1, and input in cell C1 (say). If we need the product A1 to A7, with the corresponding B1 to B7, we make cell C1 ac4ve and fill down. The automa4c upda4ng results in =A2*B2 being copied in the adjacent cell and so on. Note this method results in 7 different individual formulas being pasted into the 7 cells C1 to C7. An equivalent way uses a single array formula. We first select the range C1:C7 and then type =A1:A7*B1:B7 (which will ini4ally appear in cell C1). Since this is an array formula we press Control- ShiN- Enter rather than Enter. The formula above is entered into all the selected cells and gives the same results as previously.

20 How did it work? Because you actually wish to perform this mul4plica4on element by element you instruct Excel to do this by pressing Control- ShiN- Enter and the formula becomes {=A1:A7*B1:B7}. Excel places the brackets to indicate an array formula is being evaluated. What is actually happening? Excel is taking the 7 element array (A1:A7), and mul4plying it by the 7 element array (B1:B7), resul4ng in another 7 element array, which is placed in the highlighted cell ranges. As the result was a 7 element array, you needed to select this region before evalua4ng the formula.

21 The advantages of an array formula The second technique resulted in a single array formula in the range of cells, whereas the first technique had 7 different formulas in the range of cells. What advantage did this provide? It ensures all formulas in the range are iden4cal You cannot easily overwrite the cell formulas, because you cannot change one cell in a mul4- cell array formula.

22 Arrays and named ranges The previous examples could be made easier by giving the cell range references a name and using those as in {=Score*Weight}. There are many func4ons that expect an array in its argument eg. SUM(), AVERAGE() etc. Hence the formula =AVERAGE(Score) needs only Enter, but =AVERAGE(Score*Weight) needs Control- ShiN- Enter because the array mul4plica4on must be executed first.

23 A single cell array formula In this example we have an array formula occupying a single cell. The example {=SUM(A1:A7*B1:B7)} returns a single number. This formula works with two arrays, both of which are stored in cells. The above array formula firstly mul4plies the corresponding elements of both arrays, and creates a new array - which exists only in Excel s memory. The SUM func4on operates over the array returned by the mul4plica4on.

24 Excel macros Macros are repositories of instruc4ons (ie. a program) stored in Visual Basic modules Can have an impact on the en0re worksheet, unlike func4ons which can only return a value to a cell loca4on. Macros can affect any cell value and can automa4cally change the format of cells, cell ranges or the en4re workbook. Novices are encouraged to s4ck to simple macros. Visual Basic is not a simple language, because its API is so extensive.

25 Recording a macro A user can write a complete macro, but Excel provides the feature of automa4cally genera4ng a macro program by recording user behaviour. Use the menu sequence Tools- > Macro- > Record New Macro As you execute Excel commands, those commands are coded into a program. While recording, you are also tes4ng it and verifying that it works. The default name is Macro1, and this can be changed. When the macro starts to execute, Excel displays the macro toolbar that allows you to pause, stop and restart the macro. If you have invoked the Visual Basic toolbar, you can also control macro execu4on from it.

26 Recording a macro Use the menu sequence Tools- > Macro- > Record New Macro

27 Recording a macro Use the menu sequence Tools- > Macro- > Record New Macro

28 An example recording in the lab Select Tools- > Macro- > Record New Macro, name the macro InsertData, and make crt+i the shortcut. File- >Open, selec4ng a tab delimited data file and opening it as Tab Delimited text (follow the Wizard). Return back to the worksheet, select cell A4 and paste. Stop the macro recording, and save. Now clear the pasted data, and type crt+i, magically the data will be read from the text file, copied, closed, and pasted.

29 Viewing a macro Each macro is stored in a Visual Basic module Module sheet can be viewed by clicking the Edit bu[on of the Macros dialog box Macro Statements Green entries are comments Blue entries are keywords Black entries are Visual Basic statements Any part of the Visual Basic module can be changed Unless the changes are saved, the module is not updated

30 Problems with the recorded macro Reproduces exactly what was set when recording the macro, Hence Ø Can only ever open the same file e.g. C:\data\example- data.txt Ø Will only select the previously selected range e.g. A1:D12 in the data file. Ø Will only paste to the range star4ng at A4. These problems are solved by using the full expressive power of the Visual Basic language.

31 Go and try it!!