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# Intro to R

Hello, and welcome to my blog. The goal of this is to introduce people to R in a way that is easy to grasp. It’s command line interface can be pretty intimidating, so hopefully this can help ease you into it. Chances are, if you’re reading this, you’re a close friend of mine (I don’t have much reputation on the internet yet), but no matter who you are, I welcome comments, questions, suggestions, etc. So please speak up and tell me if you like it, ask me a question if you’re having trouble following, or leave a witty “your mom” joke!
OK, lets jump right in. If you’re going to learn R, you’re going to need to install it first. Here comes the best part – R is free!
What???
Yes, totally free! It’s an open source software, which means it’s constantly being added to and improved by an ever increasing community of programmers and enthusiasts.

#### So how to get it?

You can install just raw R and work from that, but I prefer to use a programming environment, which is just sort of a fancier way of using R that keeps everything more organized and adds sweet features such as spell check, closes parentheses and quotes for you, etc. This makes using a command line interface less intimidating. There are a few such environments available, but the one I use is R Studio so I’ll suggest you use this as well and I’ll walk you through installing it.

## Installing R

1. Go to the R website
2. Click the version of R appropriate for your computer (the options are front and center, you can’t miss them)
3. You will be given a list of further options. Mac users chose the version compatible with your current Operating System, Windows users, you want Base R and that’s it.
4. Once you’ve made the right choice on the previous page, just click “Download R 2.15.xx for (my OS)” and run the installer. You have just seriously upgraded the things your computer is capable of.
5. Go to the R Studio website
9. Save it somewhere on your computer. I put it in my Programs folder, but put it where you like.
10. What you have just downloaded is the installer, so find it where you just saved it and run the installer to actually put R Studio on your computer.

## Using R, the very basics

When you open R Studio, you’ll see three panes within the window you just opened. This is part of the organizational beauty of R Studio. The big one on the left side is your command window. This is where you interact with R. You enter something here, R evaluates it, and returns a response to you. Lets not worry about the other 2 panes yet. These are the very basics, remember?

## R as a calculator

Lets enter something into that intimidating command line. The > beckons!
Try entering:
6 * 6

[1] 36

Try:
6/3

[1] 2

Simple enough, but not particularly useful.
Now try:
6/0

[1] Inf

R returns Inf.
Now this is useful, it does not return an error, but infiniti. This is actually considered a numeric value to R, so it will not necessarily wreck your program if something ends up going to infiniti. Cool!
The multiplication and division operators in R (* and /) are intuitive and I’m sure you can go out on a limb and guess how to add and subtract as well, but what if we want to do something more complicated?
There are functions built into R that we can call to do fancier things.
Try:
sqrt(100)

[1] 10

log(10)

[1] 2.303

log10(10)

[1] 1

Cool. But now I want to get even fancier. I want to do math on a few numbers at a time. In R, if you ever want to do some operation on a group of numbers, you must concatenate those numbers.
Try entering:
1, 2, 3, 4, 5
R returns an error.
Now try using R’s concatenate function c():
c(1, 2, 3, 4, 5)

[1] 1 2 3 4 5

No error this time.
This is incredibly important. Concatenating numbers creates an object in R. You may have heard someone say that R is an object-oriented language. This is what they’re talking about. You’ve just created a very simple object. Built into R there are many, many things that you can now do with/to this object you have created.
Try:
mean(c(1, 2, 3, 4, 5))

[1] 3

Also try:
sum(c(1, 2, 3, 4, 5))

[1] 15

There are are tons of similar computations that can be don such as max(), min(), length(), sum(), median(), etc. Each of these computations is called a function. A function is different from an operator (for example the “ * ” symbol we used earlier to multiply). A function can be a lot more flexible than just a simple mathematical operation such as finding the mean, but we will discuss functions in more depth later. An operator is very rigid in function. It is purely mechanical. For example, 6 times 6 just IS 36. You add the number 6, six times, and that is the result. Now that we’ve covered concatenating numbers, lets try out some neat new operators.
Try:
c(1, 2, 3, 4, 5) * 2

[1]  2  4  6  8 10

Now we’ve done an operation on 5 numbers at a time. Sure beats typing in 5 different multiplication commands.
Now try:
c(1, 2, 3, 4, 5) * c(1, 2, 3, 4, 5)

[1]  1  4  9 16 25

See how this works? Alternatively, I could have typed:
c(1, 2, 3, 4, 5)^2

[1]  1  4  9 16 25

Now try:
c(1, 2, 3, 4, 5) %in% c(1, 2, 3)

[1]  TRUE  TRUE  TRUE FALSE FALSE

%something% is the symbol for a special operator. These usually perform some kind of element by element operations. There are a few of these in R. Notice this evaluates to a series of TRUEs and FALSEs. Once again, very mechanical. The number 1 either IS or IS NOT in the second group of numbers. Other operators that evaluate to either TRUE or FALSE are <, >, ==, <=, >=, &, |, &&, and ||. I’m sure you can guess what the first few do. Try:
3 < 6

[1] TRUE

or:
c(1, 2, 3, 4, 5) <= 3

[1]  TRUE  TRUE  TRUE FALSE FALSE

Now try using the & operator:
3 < 4 & 5 < 6

[1] TRUE

3 < 4 & 5 < 4

[1] FALSE

See what that does?
The vertical bar (acheived by holding Shift and pressing the button just above your Enter key) is the “or” operator. It works similar to the “and” operator (&):
3 < 4 | 5 < 4

[1] TRUE

The “double and” (&&) and “double or” are just programming semantics and you don't need to worry about them for now.
I'll leave you with one challenge that I'll answer in the beggining of the next post. I'll do this at the end of each post to help you learn by doing.

### Challenge:

#### Matrices:

 1 1 1 2 1 3 2 4

#### Kroenecker product:

 1 2 1 2 3 4 3 4 1 2 2 4 3 4 6 8