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sibyvt/Assignment: swirl Lesson 1: Basic Building Blocks

Created May 12, 2016 17:46
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Assignment: swirl Lesson 1: Basic Building Blocks
| 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+5
[1] 10
| One more time. You can do it! Or, type info() for more options.
| Type 5 + 7 and press Enter.
> 5+7
[1] 12
| You nailed it! Good job!
|
|====== | 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
| Excellent job!
|
|=============== | 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
| You are amazing!
|
|================== | 26%
| Now, store the result of x - 3 in a new variable called y.
> y<-x-3
| You are quite good my friend!
|
|==================== | 29%
| What is the value of y? Type y to find out.
> y
[1] 9
| Nice work!
|
|====================== | 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.
> cc(1.1, 9, 3.14)
Error: could not find function "cc"
> c(1.1, 9, 3.14)
[1] 1.10 9.00 3.14
| Give it another try. Or, type info() for more options.
| Inputting z <- c(1.1, 9, 3.14) will assign the vector (1.1, 9, 3.14) to a new
| variable called z. Including single spaces after the commas in the vector is
| not required, but helps make your code less cluttered and more readable.
> z<-c(1.1, 9, 3.14)
| Excellent work!
|
|========================== | 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
| Keep working like that and you'll get there!
|
|============================ | 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 really on a roll!
|
|============================= | 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
| All that practice is paying off!
|
|=============================== | 45%
| Numeric vectors can be used in arithmetic expressions. Type the following to
| see what happens: z * 2 + 100.
> z*2+10
[1] 12.20 28.00 16.28
| Try again. Getting it right on the first try is boring anyway! Or, type
| info() for more options.
| Enter z * 2 + 100, without assigning the result to a variable. The `*` symbol
| is used for multiplication and shares a key with the number 8 on many
| keyboards.
> z*2+100
[1] 102.20 118.00 106.28
| That's correct!
|
|================================= | 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.
> sqrt(z-1)
[1] 0.3162278 2.8284271 1.4628739
| Keep trying! Or, type info() for more options.
| Assign the result of sqrt(z - 1) to a variable called my_sqrt.
> my_sqrt<-sqrt(z-)
Error: unexpected ')' in "my_sqrt<-sqrt(z-)"
> my_sqrt<-sqrt(z-1)
| You nailed it! Good job!
|
|======================================= | 55%
| Before we view the contents of the my_sqrt variable, what do you think it
| contains?
1: a vector of length 3
2: a vector of length 0 (i.e. an empty vector)
3: a single number (i.e a vector of length 1)
Selection: 1
| You nailed it! Good job!
|
|========================================= | 58%
| Print the contents of my_sqrt.
> my_sqrt()
Error: could not find function "my_sqrt"
> print(my_sqrt)
[1] 0.3162278 2.8284271 1.4628739
| Give it another try. Or, type info() for more options.
| Just type my_sqrt and press Enter to view its value.
> my_sqrt
[1] 0.3162278 2.8284271 1.4628739
| You got it!
|
|========================================== | 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)
| Nice try, but that's not exactly what I was hoping for. Try again. Or, type
| info() for more options.
| Enter my_div <- z / my_sqrt. The spaces on either side of the `/` sign are
| not required, but can often improve readability by making code appear less
| cluttered. In the end, it's personal preference.
> my_div<-z/my_sqrt
| Keep up the great work!
|
|============================================== | 66%
| 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 nailed it! Good job!
|
|================================================ | 68%
| Go ahead and print the contents of my_div.
> my_div
[1] 3.478505 3.181981 2.146460
| Perseverance, that's the answer.
|
|================================================== | 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
| All that hard work is paying off!
|
|========================================================= | 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
| Your dedication is inspiring!
|
|============================================================= | 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.
>
> c(1, 2, 3, 4) + c(0, 10, 1000)
[1] 1 12 1003 4
Warning message:
In c(1, 2, 3, 4) + c(0, 10, 1000) :
longer object length is not a multiple of shorter object length
| Nice try, but that's not exactly what I was hoping for. Try again. Or, type
| info() for more options.
| If your environment does not support the up arrow feature, then just type the
| corrected command to move on.
> z*2+1000
[1] 1002.20 1018.00 1006.28
| Perseverance, that's the answer.
|
|================================================================== | 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
| Keep working like that and you'll get there!
|
|======================================================================| 100%
| Would you like to receive credit for completing this course on Coursera.org?
1: No
2: Yes
Selection: 2
What is your email address? [email protected]
What is your assignment token? Mj94HXH2Ty2k1bjM
Grade submission succeeded!
@Parimahajializadeh
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Very helpful, thank you

@Aus-tin
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Aus-tin commented Mar 27, 2023

very helpful, thank you so much

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