1. Lecture 21 Using & Managing Data: Spreadsheets (S&G, §§11.1–11.2)
9/22/2018 6:47 AM
Lecture 21
Using & Managing Data: Spreadsheets
(S&G, §§11.1–11.2)
9/22/2018
CS Lecture 21
CS 100

2. Some Important Applications of Computers
Spreadsheets
Databases
Symbolic & numeric computation
Networks
Artificial Intelligence
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3. Relation to Algorithms
Algorithmic problem solving is used in these applications
Algorithmic problem solving uses these applications
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4. Spreadsheet
Visual system for representing and manipulating tabular data
Often used for:
budgets & other financial data
grades
Useful for keeping dependant data consistent
Examples: Visicalc, Excel, Lotus 1-2-3
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5. Example Spreadsheet Column Cells Row Cursor 9/22/2018
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6. Cells Each cell has a “name” Cells can contain character data
e.g. “D2” is the cell in column D and row 2
Cells can contain character data
e.g., names, column headings
Cells can contain numeric data in various formats
e.g., integer, real, currency, date, time
Cells can contain formulas
e.g., “D2*E2”
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7. Relative & Fixed Cell References
A name of the form “D2” is a relative reference to the cell in column D and row 2
A name of the form “$D$2” is a fixed reference to the cell in column D and row 2
When a formula is copied into another cell:
the fixed references refer to the same cells as they originally did
the relative references refer to cells in the same relative positions
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CS Lecture 21

8. Example Suppose in G2 we have the formula: D2 * (1 + $C$8 / 100) * E2
When we copy it to G3 it will be: D3 * (1 + $C$8 / 100) * E3
When we copy it to G4 it will be: D4 * (1 + $C$8 / 100) * E4
And so forth
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9. Run Excel Spreadsheet Example
Lecture 21
9/22/2018 6:47 AM
Run Excel Spreadsheet Example
Demonstrate:
Putting formula “=D2*E2” in F2
Copying into cells below (with copy/paste)
Show how auto update
Show Pie and Bar charts (using press and hold to preview)
Select columns C & D and show scatter chart of age vs. pay rate
Insert Totals for Pay column (note the variety of available functions)
Show how auto updates
Add “Base % Increase” in B8 and 2 in C8
In col. G put “New Pay” and formula “D2*(1+$C$8/100)*E2” (may be easier to see formula in Formula Toolbar) (note dif between relative and fixed cell references)
Copy down to rest & fill in total
Apply currency formatting (Format/Cell)
Show how can change percent from 2 to 3
Insert new col. before G for Merit
Change format to General; show adjusting col. widths
Fill in new formula for NewPay col.
Show changing Base % and Merit %
Select the Pay to New Pay block and show a bar chart showing old and new Pay
Show Goal Seek (under Tools) by asking it to set H9 to 12,000 by varying C8
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CS 100

10. Beginning Spreadsheet
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11. Formula Entered in F2
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12. Result of Formula in F2
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13. Formula Copied into Rest of Column
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14. Result of Formulas in Column F
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15. Example Pie Chart of Column F
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16. Scatter Chart of Columns D vs. C
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17. Compute Sum of Column F
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18. Resulting Sum
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19. Formula for Projected Base Pay Increase
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20. Resulting New Pay
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21. Formula Relativized to Row 3
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22. Formula Relativized to Row 4
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23. Change Format of Column G
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24. Resulting Reformated Column G
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25. Insert Column for Merit Raises
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26. New Formula to Include Merit Raises
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27. Resulting Projected New Total
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28. Bar Chart of Old and New Pay
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29. Goal Seeking: Adjust Base Rate so Total = $12,000
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30. Calculated Base Rate to Meet Goal
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31. Computer Science Issues
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32. Update Strategies Reevaluate every cell
Reevaluate only those cells containing formulas
works on small spreadsheets
Reevaluate only those cells that depend on the changed cell
problem: indirect dependencies (ripple effect)
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33. Indirect Dependency
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34. Result
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35. Problem of Indirect Dependencies
Suppose change D2
Could look for all cells with a formula involving D2, and reevaluate those
But suppose F9 depends on F2, and F2 depends on D2
Bad solution:
check all cells & update those directly dependant on D2
keep a list of them
check all cells & update those directly dependent on those in list
keep a list of these, and return to (3)
continue until there are no changes
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36. Better Solution
Keep with each cell a list of all other cells directly dependant on it
Update this list whenever a formula is changed
Whenever a cell’s value is changed:
reevaluate all the cells that depend directly on it
reevaluate all the cells that depend directly on those cells
and so forth
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37. Event-Driven Programming
Lecture 21
9/22/2018 6:47 AM
Event-Driven Programming
Each cell contains either:
data
or a formula, which is a little program
these formulas are interpreted directly (not compiled into machine code)
Whenever a cell is modified:
it creates an event
which may trigger other events
must end (no circular dependencies)
There is no iteration except that provided through the built-in functions & tools
May show creating a circular reference, like C8=D8+1, D8=C8+1
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CS 100