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swirl Lesson 1: Basic Building Blocks

| Please choose a course, or type 0 to exit swirl.
1: R Programming
2: Take me to the swirl course repository!
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| Please choose a lesson, or type 0 to return to course menu.
 1: Basic Building Blocks      2: Workspace and Files     
 3: Sequences of Numbers       4: Vectors                 
 5: Missing Values             6: Subsetting Vectors      
 7: Matrices and Data Frames   8: Logic                   
 9: Functions                 10: lapply and sapply       
11: vapply and tapply         12: Looking at Data         
13: Simulation                14: Dates and Times         
15: Base Graphics             
Selection: 1
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| In this lesson, we will explore some basic building blocks of the
| R programming language.
...
  |==                                                        |   3%
| If at any point you'd like more information on a particular topic
| related to R, you can type help.start() at the prompt, which will
| open a menu of resources (either within RStudio or your default
| web browser, depending on your setup). Alternatively, a simple
| web search often yields the answer you're looking for.
...
  |===                                                       |   5%
| In its simplest form, R can be used as an interactive calculator.
| Type 5 + 7 and press Enter.
> 5+7
[1] 12
| All that practice is paying off!
  |=====                                                     |   8%
| R simply prints the result of 12 by default. However, R is a
| programming language and often the reason we use a programming
| language as opposed to a calculator is to automate some process
| or avoid unnecessary repetition.
...
  |======                                                    |  11%
| In this case, we may want to use our result from above in a
| second calculation. Instead of retyping 5 + 7 every time we need
| it, we can just create a new variable that stores the result.
...
  |========                                                  |  13%
| The way you assign a value to a variable in R is by using the
| assignment operator, which is just a 'less than' symbol followed
| by a 'minus' sign. It looks like this: <-
...
  |=========                                                 |  16%
| Think of the assignment operator as an arrow. You are assigning
| the value on the right side of the arrow to the variable name on
| the left side of the arrow.
...
  |===========                                               |  18%
| To assign the result of 5 + 7 to a new variable called x, you
| type x <- 5 + 7. This can be read as 'x gets 5 plus 7'. Give it a
| try now.
> x<-5+7
| Keep working like that and you'll get there!
  |============                                              |  21%
| You'll notice that R did not print the result of 12 this time.
| When you use the assignment operator, R assumes that you don't
| want to see the result immediately, but rather that you intend to
| use the result for something else later on.
...
  |==============                                            |  24%
| To view the contents of the variable x, just type x and press
| Enter. Try it now.
> x
[1] 12
| Nice work!
  |===============                                           |  26%
| Now, store the result of x - 3 in a new variable called y.
> y<-x-3
| You got it!
  |=================                                         |  29%
| What is the value of y? Type y to find out.
> y
[1] 9
| All that practice is paying off!
  |==================                                        |  32%
| Now, let's create a small collection of numbers called a vector.
| Any object that contains data is called a data structure and
| numeric vectors are the simplest type of data structure in R. In
| fact, even a single number is considered a vector of length one.
...
  |====================                                      |  34%
| The easiest way to create a vector is with the c() function,
| which stands for 'concatenate' or 'combine'. To create a vector
| containing the numbers 1.1, 9, and 3.14, type c(1.1, 9, 3.14).
| Try it now and store the result in a variable called z.
> z<-c(1.1,9,3.14)
| Perseverance, that's the answer.
  |=====================                                     |  37%
| Anytime you have questions about a particular function, you can
| access R's built-in help files via the `?` command. For example,
| if you want more information on the c() function, type ?c without
| the parentheses that normally follow a function name. Give it a
| try.
> ?c
| Nice work!
  |=======================                                   |  39%
| Type z to view its contents. Notice that there are no commas
| separating the values in the output.
> z
[1] 1.10 9.00 3.14
| You are amazing!
  |========================                                  |  42%
| You can combine vectors to make a new vector. Create a new vector
| that contains z, 555, then z again in that order. Don't assign
| this vector to a new variable, so that we can just see the result
| immediately.
> c(z,555,z)
[1]   1.10   9.00   3.14 555.00   1.10   9.00   3.14
| That's correct!
  |==========================                                |  45%
| Numeric vectors can be used in arithmetic expressions. Type the
| following to see what happens: z * 2 + 100.
> z*2+100
[1] 102.20 118.00 106.28
| That's the answer I was looking for.
  |===========================                               |  47%
| First, R multiplied each of the three elements in z by 2. Then it
| added 100 to each element to get the result you see above.
...
  |=============================                             |  50%
| Other common arithmetic operators are `+`, `-`, `/`, and `^`
| (where x^2 means 'x squared'). To take the square root, use the
| sqrt() function and to take the absolute value, use the abs()
| function.
...
  |===============================                           |  53%
| Take the square root of z - 1 and assign it to a new variable
| called my_sqrt.
> my_sqrt<-sqrt(z-1)
| You got it right!
  |================================                          |  55%
| Before we view the contents of the my_sqrt variable, what do you
| think it contains?
1: a vector of length 0 (i.e. an empty vector)
2: a vector of length 3
3: a single number (i.e a vector of length 1)
Selection: 2
| You are quite good my friend!
  |==================================                        |  58%
| Print the contents of my_sqrt.
> my_sqrt
[1] 0.3162278 2.8284271 1.4628739
| You are quite good my friend!
  |===================================                       |  61%
| As you may have guessed, R first subtracted 1 from each element
| of z, then took the square root of each element. This leaves you
| with a vector of the same length as the original vector z.
...
  |=====================================                     |  63%
| Now, create a new variable called my_div that gets the value of z
| divided by my_sqrt.
> my_div<-z/my_sqrt
| You nailed it! Good job!
  |======================================                    |  66%
| Which statement do you think is true?
1: The first element of my_div is equal to the first element of z 
divided by the first element of my_sqrt, and so on...
2: my_div is a single number (i.e a vector of length 1)
3: my_div is undefined
Selection: 1
| Great job!
  |========================================                  |  68%
| Go ahead and print the contents of my_div.
> my_div
[1] 3.478505 3.181981 2.146460
| Your dedication is inspiring!
  |=========================================                 |  71%
| When given two vectors of the same length, R simply performs the
| specified arithmetic operation (`+`, `-`, `*`, etc.)
| element-by-element. If the vectors are of different lengths, R
| 'recycles' the shorter vector until it is the same length as the
| longer vector.
...
  |===========================================               |  74%
| When we did z * 2 + 100 in our earlier example, z was a vector of
| length 3, but technically 2 and 100 are each vectors of length 1.
...
  |============================================              |  76%
| Behind the scenes, R is 'recycling' the 2 to make a vector of 2s
| and the 100 to make a vector of 100s. In other words, when you
| ask R to compute z * 2 + 100, what it really computes is this: z
| * c(2, 2, 2) + c(100, 100, 100).
...
  |==============================================            |  79%
| To see another example of how this vector 'recycling' works, try
| adding c(1, 2, 3, 4) and c(0, 10). Don't worry about saving the
| result in a new variable.
> c(1,2,3,4)+c(0,10)
[1]  1 12  3 14
| You got it right!
  |===============================================           |  82%
| If the length of the shorter vector does not divide evenly into
| the length of the longer vector, R will still apply the
| 'recycling' method, but will throw a warning to let you know
| something fishy might be going on.
...
  |=================================================         |  84%
| Try c(1, 2, 3, 4) + c(0, 10, 100) for an example.
> c(1,2,3,4)+c(0,10,100)
[1]   1  12 103   4
Warning message:
In c(1, 2, 3, 4) + c(0, 10, 100) :
  longer object length is not a multiple of shorter object length
| Excellent work!
  |==================================================        |  87%
| Before concluding this lesson, I'd like to show you a couple of
| time-saving tricks.
...
  |====================================================      |  89%
| Earlier in the lesson, you computed z * 2 + 100. Let's pretend
| that you made a mistake and that you meant to add 1000 instead of
| 100. You could either re-type the expression, or...
...
  |=====================================================     |  92%
| In many programming environments, the up arrow will cycle through
| previous commands. Try hitting the up arrow on your keyboard
| until you get to this command (z * 2 + 100), then change 100 to
| 1000 and hit Enter. If the up arrow doesn't work for you, just
| type the corrected command.
> z*2+1000
[1] 1002.20 1018.00 1006.28
| All that practice is paying off!
  |=======================================================   |  95%
| Finally, let's pretend you'd like to view the contents of a
| variable that you created earlier, but you can't seem to remember
| if you named it my_div or myDiv. You could try both and see what
| works, or...
...
  |========================================================  |  97%
| You can type the first two letters of the variable name, then hit
| the Tab key (possibly more than once). Most programming
| environments will provide a list of variables that you've created
| that begin with 'my'. This is called auto-completion and can be
| quite handy when you have many variables in your workspace. Give
| it a try. (If auto-completion doesn't work for you, just type
| my_div and press Enter.)
> 
> my_div
[1] 3.478505 3.181981 2.146460
| You are quite good my friend!
  |==========================================================| 100%

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