# Basic Building Blocks

swirl()

| Welcome to swirl! Please sign in. If you've been here before, use the same name as you
| did then. If you are new, call yourself something unique.

What shall I call you? Krishnakanth Allika

| Please choose a course, or type 0 to exit swirl.

1: R Programming
2: Take me to the swirl course repository!

Selection: 1

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

| In its simplest form, R can be used as an interactive
| calculator. Type 5 + 7 and press Enter.

5+7
[1] 12

|==== | 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 up the great work!

|============ | 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

|=============== | 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

| You are doing so well!

|================== | 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)

| That's the answer I was looking for.

|===================== | 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

| That's correct!

|====================== | 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 quite good my friend!

|======================== | 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

| Excellent work!

|========================= | 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

| You are amazing!

|=========================== | 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)

| Nice work!

|=============================== | 55%
| Before we view the contents of the my_sqrt variable, what do you
| think it contains?

1: a single number (i.e a vector of length 1)
2: a vector of length 0 (i.e. an empty vector)
3: a vector of length 3

Selection: 3

| Excellent work!

|================================= | 58%
| Print the contents of my_sqrt.

my_sqrt
[1] 0.3162278 2.8284271 1.4628739

| You're the best!

|================================== | 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

|===================================== | 66%
| Which statement do you think is true?

1: my_div is a single number (i.e a vector of length 1)
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 undefined

Selection: 2

|======================================= | 68%
| Go ahead and print the contents of my_div.

my_div
[1] 3.478505 3.181981 2.146460

| You got it!

|======================================== | 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

| Excellent work!

|============================================== | 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
| 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

| Keep up the great work!

|====================================================== | 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're the best!

|=========================================================| 100%
| Would you like to receive credit for completing this course on
| Coursera.org?

1: No
2: Yes

Selection: 2