R Essential Definitions
- Define the following terms, and identify them in an R expression:
- assignment
- variable name
- function call
- argument
- Find and interpret builtin documentation
- Search for error messages
Assignment
?`=`
Assign x to 3
x = 3
x <- 3 # Does same thing
x is the variable name, and 3 is the value.
Print it out, see the current value.
x
What’s that [1] doing in front of our 3?
Here’s a hint:
1:50
x is defined, so we can use it in calculations.
Q: make a prediction, what’s the result below?
x = 3
x + 4
We see x in our global environment, assigned to the value 3.
Q: below we assign x to a different value, 5.
Make a prediction, what will the line below produce?
x = 5
x + 4
We can change x, and use the new value.
Q: How do we assign the x + 4 to the variable y?
y = x + 4
In general, we can put as many computations as we need to on the right.
y = 5*(x-5) + 4 + x^2 - 2.2
Function calls
Functions are the heart of R. Next week, we’ll start defining our own functions. Function calls typically look something like this:
sqrt(4)
Q: Guess what this does?
sqrt is the function, and 4.2 is the argument.
A function can accept 0, 1, or many arguments.
Documentation
To learn exactly what sqrt does, we need to look at the documentation.
?sqrt
Demo documentation.
Errors
Suppose we write something incorrect: Q: Make a prediction, what will happen?
sqrt(four)
This happens because four is a name, not a literal like 4.
Suppose you have no idea what this error message means.
The obvious solution is to Google it.
Q: How do you Google it? The whole error message, or modify it? How to modify it? Take out part specific to your problem. Google this: “Error: object not found”
Here’s the first Stack Overflow post Google found for me. The answer goes into great detail about all the possible ways you could produce this error.
packages
“There’s an app for that” External, user contributed packages make R great. CRAN has tons, for every application you can imagine. Explain package GUI.