Homework 1-1

Due: January 30, 11:59 pm

Reminders

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 exceptions to this rule are problems marked as “(Independent)”. You may only discuss independent problems with course staff.

Basics

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 1-11 will give you an introduction to spreadsheets and serve as good background.
  2. Tasks 12 describes the spreadsheet you will need to hand in

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 work 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 and 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 labeled “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. Observe 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

“The forms of things unknown, the poet's pen / Turns them to shapes, and gives to airy nothing / A local habitation and a name.” (Shakespeare, A Midsummer Night's Dream, V.i.15-17). See also Naming of Parts, by Henry Reed.

Naming things is one of the ways that we impose structure on the world. While Google spreadsheets have 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:

  1. On the menu at the top of the screen, click data, and then select the button that says "Named ranges".
  2. Click "+Add a range" of the new window that just popped up. The speadsheet will prompt you to enter a name, and choose one or more cells that the name will refer to. Use "age" for the cell name and to specify the cell, use "Sheet1!A2". Now click "Done". Cell A2 is now named "age". Big efficiency hint: Use the Tab key to quickly select different spaces. In this case, after you click the + to add a new range, you will have the name selected. After you enter in a name, using Tab will select the range for you, and using it again and pressing Enter will click the little grid in the second text box, allowing you to manually select cells from the spreadsheet to name! After you select your cell(s) and click ok, tabbing two more times will allow to hit done with one last Enter key. This all might seem weird and a little pointless, but realize that tabbing can be used in most applications, and the seconds you save in repeated processes from not moving your hand between mouse and keyboard will add up quickly. Also, if you overshoot something, use Shift + Tab to go backwards.
  3. Click on B2, and enter the formula =age; the result should be that your age appears in cell B2.
  4. Click on cell B2 and enter the formula =A2; again, your age should appear. The cell A2 can be referred to either by its standard spreadsheet address (A2), or by its name (“age”).
  5. Go to Sheet2, and in cell B2, type a formula that will copy your age from Sheet1, cell A2. Use the name “age” rather than “A2”.

Point of Information: Renaming Sheets

Click on the Sheet3 tab. If there is no Sheet3 you can create one by clicking on the plus sign at the left of Sheet1. 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".


Descriptions

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:

Right-click on cell A2 of Sheet1. Select Insert note. Type Enter your age in this cell as a note. Notice:

  1. A small black triangle appears in the upper right of the cell to indicate there's a note for the cell.
  2. When you hover your mouse cursor over the cell, the note appears.

Filling

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:

  1. Review the next portion of the tutorial on using “Fill Handles.”

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 multiple 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:

Work through the tutorial's “Lesson 12: Creating Simple Formulas”.

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: when you tell a friend how to get to your home, you might say something like “Take route 42 for the first 8 miles. If it's rush hour, take 302 to go around the city; if not, just take route 42 straight through the city. On the other side, whichever route you took, watch for signs for Millville, and take the first Millville exit...” 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:

  1. In cell D1 on Sheet 1, enter 12. In cell D2, enter the formula: =If(D1 > 10, 3, 0). Observe the result. Change the value of D1 to 4, and observe the result.

  2. An Explanation of Conditionals

    The If expression checks to see whether D1 is greater than 10; if so, the value of the If expression is 3; if not, its value is 0. The “condition” (the bit of code before the first comma) can use equality-testing (If(D1 = 3, ...)), various inequalities (If(D1 >= 2, ...), If(D1 < 5, ...)), or even other functions (If(IsBlank(D1), ...)). This last test determines whether cell D1 has anything in it or not, using the ISBLANK() function.

    The value-if-true can also be more complicated than a single number. For instance, the expression =If(D1 < 5, D1+3, D1-2) gives D1+3 if D1 is less than five, but if it's five or more, the expression gives D1-2.

  3. Nesting Conditionals

    But what if we want something different to happen when D1 = 5? Now we have 3 desired outcomes, and a single IF isn't enough to handle this. What do we need to change to fix this? Consider the problem. We effectively want to split the "is not less than 5" answer into "is equal to 5" and "is greater than 5". What we want is another IF statement inside of our first IF statement. Putting functions inside of each other is called nesting functions, and in the case of IF's, it's a great way to deal with 3 or more conditional outcomes. Try replacing the last argument of your IF statement with IF(D1 = 5, D1, D1 - 2) so that you end up with IF(D1 < 5, D1+3, IF(D1 = 5, D1, D1 - 2)). When you change the value of D1 from 4 to 5 to 6 (and if you get an error, double-check that both statements are closed with parentheses; you should have 2 at the end of the formula).

  4. Point of Information: Syntax in Google Spreadsheets

    If the syntax in the box above is confusing to you, don't worry! There are two ways that we can learn more information about the built-in expressions and functions like IF in spreadsheets:
    • When you begin typing the “=If” in the formula bar, you will see a box pop up below the bar showing something like IF(logical_test, [value_if_true], [value_if_false]). This is the program's way of letting you know what values it is expecting within the parentheses following the IF expression. In this case, the first thing we enter after the =IF(, also called an argument or a parameter, is the logical test D1 > 10, which evaluates to be either true or false. The second parameter, as described above, tells the spreadsheet what to place in cell D2 if the logical test is true (the value in cell D1 is greater than 10). The third parameter tells the spreadsheet what to place in cell D2 if the logical test is false (the value in cell D1 is less than 10). So, if the value in cell D1 is 4, we can see that the logical test evaluates to false, and so the value in cell D2 will be set to 0.
    • To learn even more information about a function or expression that you wish to use, you can click on the expression that pops up below the formula bar as you are typing (in this case the IF). This will bring you to a help page on this function, which happens to be online as well. This information is helpful to read if you aren't sure what each parameter means, and often includes examples of the function's use. Here's a list of the many functions that you may later use in your adventures. Try looking up the information page for the ISBLANK function described in Part 2 above.
  5. Point of Information: Capitalization in Google Spreadsheets

    When we are writing expressions and formulas in spreadsheets, the capitalization most often doesn't matter. This means that you may see the IF expression written as If, if, or even iF, and they all are equivalent and will accomplish the same thing (although either of the first two is standard and recommended). It is important to note that in most other programming languages, including Python (which we will see in the second half of the course), capitalization is critical to the meaning of the code, unlike in spreadsheets.


Pivot Tables

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 senate, and every so often we have a vote; each senator casts a vote. Or we're running Netflix, and every so often a customer rents a movie.) Our data might look like this (for a very small class):

NameWeekQuizScore
Amy180
Mary172
Robin190
Amy285
Robin291
Mary265
Mary279
Robin290
Amy270
Mary390
Robin380
Amy379

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:

NameWeek1Week2Week3
Amy8077.579
Mary.........
Robin.........

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 10:

  1. Work through this tutorial: “Creating Pivot Tables”.

A Note About Pivot Tables

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, by a little subterfuge: suppose you replaced each A with a 5, each B with a 4, 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 5s, 4s, 3s, etc. That's not ideal. So what can we do? We can take the table and replace all of the 5s with As, 4s 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 senators' votes on various bills. Each senator gets exactly one vote (Yea/Nay/Not Voting) 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.


Task 11

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. Try this out in your spreadsheet.

Task 12:

  1. Once you have completed the tutorials and above exercises, make a copy of HW1-1 (click on the link; it is a different spreadsheet than the one you've been working on so far) by clicking File, then "Make a copy" and store it in your Google Drive.
  2. Rename your file to something like JohnSmith_HW1-1 (i.e., your name, followed by “HW1-1.”).
  3. This spreadsheet file will contain several exercises. Complete the tasks in the spreadsheet.
  4. You will share this file to the TAs (cs0030handin@gmail.com) at the end of this homework.

Final Handin

Congratulations, you're done with your first assignment! Share the HW1-1 spreadsheet you copied and completed with the TAs cs0030handin@gmail.com. We do not need to see the spreadsheet you used for tasks 1-11. Make sure your submission contains your first and last name in the file name! In the above file names, “FirstLast” should be replaced with your first and last name or we will take off points. Make sure every task has been completed.