Homework 1-1

For the following problems you may discuss the concepts that will help solve these problems with classmates and course staff. You may not simply copy down the answers of your classmates as that is a violation of the collaboration policy. The one exception to this rule are those problems marked as “(Independent)”. You may discuss independent problems with the teaching team only.

These problems should take you just a few minutes each; each one aims to teach you a particular skill that you'll need to have with spreadsheets. Most involve a task and some hint of how to approach it; you'll want to do a web search, or ask a friend, or use the Help menu from the toolbar to learn how to do things.

One good reference is this google spreadsheets tutorial. In fact, several of the following problems involve parts of it; if you have some time, it is definitely worth working through the whole thing over the next week or two.

This homework may seem long, but don't get intimidated! Most of the assignment is a tutorial, and the problems themselves are very easy. If you are already comfortable with spreadsheets, feel free to skim over the tutorials and focus mainly on anything that you are not familiar with. There is also a required handin at the end of the assignment that will test most of the subjects covered in this tutorial.

1. Tasks 1-9 will give you an introduction to spreadsheets and serve as background for later tasks.
2. Task 10 will complete the first file of your handin.
3. Tasks 11-14 will complete the second file of your handin.

This homework will also be a great reference for you to look back on as we progress through the course, because there are many points of information and hints that may be helpful in later assignments, so keep that in mind!

Task 1:

Go to the tutorial and read through "Google Sheets" Lessons 8-11. When you're done, you should know how to move around in a spreadsheet, enter data into cells, delete data from cells, select a region of cells, how to save and close a spreadsheet, and even how to format cells.

Task 2:

Now we're going to enter a formula in a cell. Formulas are the heart of spreadhsheets, but for now we're doing something very simple.

1. First enter your name in cell A1. Then click on cell B1, and in the formula bar, type

   =A1

   and hit Enter. The equals sign is essential; it tells the spreadsheet that you're entering a formula rather than just a piece of text like your name. When you hit Enter, cell B1 should show your name, just as cell A1 does. Now click on cell C1 and in the formula bar, type

   A1

   (notice that there's no equals-sign). Press Enter. Cell C1 should display the text “A1”.
2. Now go to cell A1 and enter a different name. Notice that cell B1 also changes. That's because the rule defining B1 is that it “equals whatever's in A1”. The rule defining A1 is that it's “Robin Smith” (or whatever you typed in there). Change cell A1 back to your own name.
3. Suppose that for some reason, you wanted cell C1 to contain the letters “=A1” (that is to say, an equals sign, followed by a capital A, followed by the numeral “1”). If you tried to type this into cell C1, the spreadsheet would see the equals sign and interpret it as a formula. What can you do? This is a special case: you can type a single quote, and then “=A1”, i.e., you enter

   '=A1

   and it'll turn it into what you want. You'll probably never need to do this, but you should try it once just to see that it works.

Task 3:

At the lower-left of the spreadsheet, you'll notice a tab labelled “Sheet1”. When your spreadsheet opens up, you're looking at Sheet1, and more sheets can be created by clicking the + button next to the sheet name. Enter your name in cell A1 (it may still be there from Task 2). Now click the + button; you'll see a fresh spreadsheet in which cell A1 is empty. Enter a friend's name in cell A1. Click on the Sheet1 tab, and then on the Sheet2 tab.

In cell A2 in Sheet1, decribe what you see in cell A1 after each click.

Task 4:

If you go to Sheet2, and in cell B1 you enter =A1, the value that will appear in cell B1 will be your friend's name. That's because cell-addresses refer to the current sheet. But you can enter a formula that lets you get at cells from another sheet. On Sheet2, click on cell B1. Enter the formula

=Sheet1!A1

and press Enter. Your name should show up in cell B1, having been copied from cell A1 on Sheet1. Go to Sheet1, cell A2, and enter your age. Notice that it appears all the way to the right in cell A2 because your spreadsheet has interpreted it as a number, and numbers, by default, are shown "right justified" in spreadsheet cells.

Naming things is one of the ways that we impose structure on the world. While google spreadsheets has default names (like “A1” or “N13”) sometimes it makes sense to give things names that are more readable by humans. For instance, the contents of cell A2 (your age), might be better called “age” than “A2.” Here's how to add a name to a cell:

Task 5:

Point of Information: Renaming Sheets

Click on the Sheet3 tab. Then click on the small arrow on the right of the tab. A menu pops up; click Rename and rename it “Junk”. You'll see the name change on the tab. The same can also be accomplished by double-clicking on the tab name. Try this, and change the name back to “Sheet3”. Hint: Don't name sheets with spaces, otherwise referring to them in your formulas will become ugly. Use names like "My_Finances" instead of "My Finances".

When you build a spreadsheet, you're doing so with some intent. You should record your intentions by adding notes to your spreadsheet(s).

Task 6:

Let's talk about “Filling” — taking some data from a cell or two, and using it to generate data for a whole bunch of cells. Filling is kind of like a fancy copy/paste operation. We'll do this by example in the next task.

By the way, cutting, pasting, and copying work in spreadsheets much as they do in many other programs, with a few subtle differences that you'll learn about.

A Useful Side Note: Keyboard Shortcuts

A useful shortcut is to highlight whatever it is you wish to copy, and then press the Ctrl and C keys on the keyboard to copy the text (On Macs, use Command instead of ctrl for most of these instructions). Then move your cursor to wherever you wish to paste, and hit the Ctrl and V keys to paste. If you haven't done this before, try it out in any program, even while writing an email, for example. Keyboard shortcuts are extremely useful and once you learn them, they will save you a lot of time!

Now let's try copying and pasting in a way that is unique to spreadsheets: by filling.

Task 7:

Another Side Note: More Keyboard Shortcuts

There are also keyboard shortcuts involved with filling! If you highlight all the cells you want to fill (including the initial one) and press the Ctrl (or Command if you're on a Mac)and Enter keys, the selection should automatically fill down and/or right for you.

If you would like to select mulitple cells using only the keyboard, there are shortcuts for that, too. If you've selected a cell and want to highlight a series of cells below that, pressing the Shift and the down arrow (or the arrow of whatever direction you want to highlight) for however many cells you want to highlight will do that for you. If you want to select multiple cells that aren't necessarily grouped together on the spreadsheet, you can do this by holding down the Ctrl key and clicking on all the cells you want to highlight.

Finally, if you want to highlight a whole range of occupied cells, pressing Ctrl, Shift, and an arrow key will automatically highlight all the occupied cells in the arrow's direction from the initial cell, i.e. if there are 15 occupied cells grouped together in a column, if you select the top cell and press Ctrl, Shift, and the down arrow, all 15 cells will be automatically highlighted. If there are no occupied cells in the direction of the arrow key, you'll end up highlighting all the blank cells to the end of the sheet/to the next occupied cell.

If you would like to learn more keyboard shortcuts for Google Spreadsheets, here's a handy guide you can look at

Task 8:

There's great power in establishing a bunch of relationships, and then seeing what happens when you change one cell. (“What would the company profits be if we could reduce the cost of manufacturing widgets by three percent?”) The formulas you've already encountered let you do things like that. But one kind of formula adds a special power to a spreadsheet: the conditional formula, which usually involves an IF.

Here's how it works: suppose you are giving your friend directions on how to get to PolyU from the airport. You might say something like “Take the A22 from the airport, get off at Wylie Road and then walk the last 1.2 km. If it's rush hour and you don't want to get stuck in traffic, take the Airport Express to Kowloon station and then take a taxi from there. ” This is a conditional description: what your friend should do depends on whether or not it is rush hour. So rush-hour-ness is the condition, and there are two choices for what to do: one if it is rush hour, and one if it isn't.

In writing expressions in speadsheets, we don't do things so much as we express computations: for example, “Cell A3 should be the sum of cells A1 and A2”. How can a notion of conditionality fit into this? This isn't something you see in algebra class, so we have to write it a little differently. Let's see an example:

Task 9:

Task 10:

Throughout this course, we'll tend to work with very organized data. It'll be very common to have lots of instances that are very similar, which we can organize in columns. For example, suppose we have records for a class: each week we have a quiz or two, and each student gets a grade. (Equivalently, we have a Legislative Council, and every so often we have a vote; each legislator casts a vote.) Our data might look like this (for a very small class):

We've entered the grades into our spreadsheet in the order the papers happened to fall during grading, so some weeks Amy is first, other weeks Mary is first, etc. Notice that in week two, we had two quizzes rather than just one.

This spreadsheet is a kind of database, in the sense that it's a bunch of records, where each record provides information about a single name/week/quiz score. The key thing about these records is that each consists of the same three things: a name, a week, and a quiz score. These three things are called fields in the database. (We'll see databases quite a lot more later in the course, so this is just a nice easy example to get you used to some terminology.)

Now imagine that we'd like a summary of each student's average performance, by week. We want a table that looks like this:

To do this, we can create what's called a “pivot table,” and Google Spreadsheets has a tool that can produce this for us.

Task 11:

There's one tricky thing about pivot tables: they only work for summarizing numbers. For example, if you have a table of letter grades (A, B, C, etc.), then things like “max” and “min” and “average” won't make sense, and a pivot table will be of no use to you. You can still create one, however, with a little trick: suppose you replaced each A with a 4, each B with a 3, and so on, converting each letter grade to a number on a GPA-like scale. Then you could compute the maximum grade, or the minimum. The “average” would not make sense. You could compute it, but it would have no real meaning. (Why not?)

When you have your pivot table displaying the maximum grades, however, you'd have a table full of 4s, 3s, 2s, etc. That's not ideal. So what can we do? We can take the table and replace all of the 4s with As, 3s with Bs, and so on, converting each GPA number back into a corresponding letter grade. Here is a summary of what we have just done:

1. Convert the letter grades to their numerical representations.
2. Make a pivot table based on these numerical representations.
3. Convert the pivot table results back to the corresponding letter grades.

There's one case where this convert-pivot-convert-back approach is especially effective: when each entry in the pivot table corresponds to exactly one row in the input table. For instance, in class we'll look at legislators' votes on various bills. Each senator gets exactly one vote (Yes/No/Abstain) on each bill. In this case, the operation that is done on each cell (i.e., “max”, “min”, or “average”) will always end up computing that single vote.

You have already seen the addition of the values of two cells in speadsheets, but sometimes you would like to combine the contents of two cells in other ways. If you have foo in cell A1 and 42 in cell A2, you can make foo 42 in cell A3 by typing = A1 & " " & A2 into A3. The & operation combines two strings of characters by concatenating them.

Task 12:

Task 13:

Task 14: