Inputting commands into R

You can input commands into R through …

• … the console
• … a script
• … an R-notebook
• …

The console

Let start by opening our console in RStudio.
How would we do the following:

• Do simple arithmetic: add, subtract, multiply, divide?
• Assign a value to a variable?
• Take the natural logarithm of 10?
• Exponentiate 2?
• Take the square root of 4?
• Take the third root of 27?

The console (cont’d)

• If you define a variable in a command in the console, it will remain available in all the subsequent commands (look at the environment in the upper right)
  1. Assign the value 7 to variable x
  2. Assign the value 9 to variable y
  3. Define z to be the sum of x and y
  4. Print out the value of the square of z
• This is the perfect place to ask for help

Vectors

• We already know how to assign values to variables
• How do we create vectors?
• Use the concatenation operator c
• Let’s go into the console and play with it

The concatenation operator

• Create a vector x with values 1,4,9
• Create a vector y with values 1,8,27
• Concatenate vectors x and y into vector z and print it out
• Create a vector p of names of Generation I starters
• Print out your vector p

Vectors of equally spaced numbers

• We use the colon : to make vectors of consecutive numbers
• See what happens when you run 1:10
• See what happens when you run -10:0
• What if you want to list numbers in increments of 5?
• Seek help for command seq
• Now, create a list of numbers from 1 to 25 increasing by 4

Functions and operations on vectors

• Vectorization: if you give a function a vector (or vectors) as an argument, the returned value will be a vector of results of that operation performed element by element
• Print out the list of cubes of the first consecutive 5 natural numbers

More functions and operations on vectors

• What if you want to multiply two vectors?
• Create a vector q of 1,2,3
• Create a vector e of -1,1,2
• Add q and e; what do you get?
• Multiply q by e; what do you get?

Recycling

• If you try to add up or multiply vectors of different lengths, the shorter one gets “recycled”
• This is useful when the short vector is of length 1
• Print out the list of the first 12 even numbers
• Pick your favorite 4 non-zero digits; put them in a vector t
  
• Pick your other favorite 4 digits; put them in a vector o
  
• Print out a vector of 4 numbers with the tens digits from t and the ones digits from o (paired up element by element)

Extracting parts of vectors

• What if you just want a part of a vector?
• Then you use the indexing operator []
• Let’s practice what it does
• Define the vector x as the first 5 natural numbers
• How do you extract the first element in x?
• How about the second and the fourth elements in x?
• How about all but the third element in x?
• What if you want to repeat elements?

Extracting parts of vectors

• Caveat #1: Counting starts from 1
• Caveat #2: Negative numbers mean complementation, not counting from the back
• Caveat #3: The contents of [] must be a vector itself; a nice consequence is that this means that we can input conditions for whether we keep an element or not

Scripts

• What if you do not want to use R simply as a calculator?

• Then you use scripts: text files that hold R code (with extension .R)

• You can run scripts as a whole or just parts by highlighting

• Scripts can be saved

Creating scripts

• Now, go to File->New File->R Script

• A new pane in the upper left corner, just above the console should appear: that’s your script editor

• Now, let’s write a script that calculates the sum of the first 25 odd numbers

Running scripts

• If you want to run a single line, go to it and click Run
• If you want to run an interval of lines, highlight them and click Run
• If you want to run the whole script, click Source
• Your output will appear in the console

R Notebooks

• These are text files containing chunks of R code mixed with regular text
• Let’s try to see what happens if we create one
• Go to File->New File->R Notebook