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1: R Programming
2: Take me to the swirl course repository!
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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
| | 0%
| 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
| You are doing so well!
|===== | 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.
...
|======== | 14%
| 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.
...
|=========== | 19%
| 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
| That's correct!
|============ | 22%
| 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
| That's correct!
|=============== | 27%
| Now, store the result of x - 3 in a new variable called y.
> y<-x-3
| Your dedication is inspiring!
|================= | 30%
| 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.
...
|==================== | 35%
| 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)
| Excellent job!
|===================== | 38%
| 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
| You are amazing!
|======================= | 41%
| 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
| All that hard work is paying off!
|======================== | 43%
| 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
| You got it!
|========================== | 46%
| 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
| Nice work!
|=========================== | 49%
| 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.
...
|============================= | 51%
| 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.
...
|============================== | 54%
| Take the square root of z - 1 and assign it to a new variable
| called my_sqrt.
> my_sqrt<-sqrt(z-1)
| You are quite good my friend!
|================================ | 57%
| Before we view the contents of the my_sqrt variable, what do
| you think it contains?
1: a vector of length 3
2: a single number (i.e a vector of length 1)
3: a vector of length 0 (i.e. an empty vector)
Selection: 1
| Keep up the great work!
|================================= | 59%
| Print the contents of my_sqrt.
> my_sqrt
[1] 0.3162278 2.8284271 1.4628739
| You are quite good my friend!
|=================================== | 62%
| 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.
...
|==================================== | 65%
| Now, create a new variable called my_div that gets the value of
| z divided by my_sqrt.
> my_div<-z/my_sqrt
| Perseverance, that's the answer.
|====================================== | 68%
| Which statement do you think is true?
1: my_div is undefined
2: 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...
3: my_div is a single number (i.e a vector of length 1)
Selection: 2
| You got it right!
|======================================= | 70%
| Go ahead and print the contents of my_div.
> my_div
[1] 3.478505 3.181981 2.146460
| Your dedication is inspiring!
|========================================= | 73%
| 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.
...
|========================================== | 76%
| 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.
...
|============================================ | 78%
| 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).
...
|============================================= | 81%
| 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
| Great job!
|=============================================== | 84%
| 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.
...
|================================================ | 86%
| 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
| Nice work!
|================================================== | 89%
| Before concluding this lesson, I'd like to show you a couple of
| time-saving tricks.
...
|=================================================== | 92%
| 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...
...
|===================================================== | 95%
| 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!
|====================================================== | 97%
| 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...
...
|========================================================| 100%
| 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!
| Are you currently enrolled in the Coursera course associated
| with this lesson?
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