R Programming
How to create a matrix from vector?
Using vector function. dim(m) <- vector (c(rows, columns))
Rows and columns in a Matrix are like which object?
Vector
Scope
When you use a variable, either in an expression or for assignment, it should be in scope. For an existing variable, scope defines when such variable is available. For a newly assigned variable, the scope is established at assignment.
Get working directory
getwd()
How many values in a vector?
length(vetor)
Set working directory
setcwd()
See structure of an object (data structure)
str() Function
Function
A logical unit of processing code. Usually represents some work that is encapsulated to be reused. Returns the result of processing to the caller.
variables are references to?
Data structures (data objects) and functions (code objects)
Class of object
Data type of the object. E.g. Character, Integer, Logical
How do you see the dimensions of a matrix?
Dim(matrix object)
How is list related to vector?
Each element of a list is a vector. So, a list can be considered a collection of vectors.
Text editor
Editor to create and work with plain text files. Text files are saved with .txt extension by convention.
Two parenthesis after function name
Executes the function
What is a working directory?
If you don't explicitly specify one, a folder on your computer where R will look for files - both to read and write.
Coercion
Implicit or explicit conversion of one data type (class) to another
Arguments
Parameters values passed in between parenthesis, to the function
Clearing workspace does what?
Removes all the variable references to data structures and functions
Clear console
Rstudio: Ctrl+L R GUI: Alt+Ctrl+L
Symbol for: Multiplication Division Exponent
Symbol for: Multiplication: * Division: / Exponent: ^
Get Help
?Command help(command) To start searchable help page: help.start()
Data Structure
A complex data type, typically composed of more than one value. In R, the main data structures are: Vector, Factor, Matrix, List, Data Frame
Variable
A symbol to which we assign a value. This can be a simple value, or a complex data structure that consists of many individual values. The symbol then can be used elsewhere instead of the value. The value is typically assigned as a result of an expression. An expression may use other variables that have been previously assigned.
What is a matrix?
A two dimensional vector which has values of the same class
Vector
An object that can store one or more values of the same class (data type)
Parameters
Arguments expected by a function
How do you explicitly coerce a class/datatype to another?
By using the *. function
y <- c("a", TRUE) is coerced to?
Character
Assignment operator
Conventionally, <- is used. e.g., below statement assigns value 5 to a variable x, x <- 5
What happens when you have numbers in a character vector?
It gets stored as a character
What is a list?
List is a collection of vectors
How is matrix related to vector?
Matrices are vectors in either dimension. Each Row and column represents a vector
What are attributes of R objects (data structures)
Metadata that describes other properties of an object. E.g. class, length etc.
What does dim(matrix object) produce?
Number of rows,columns in the matrix
y <- c(TRUE, 2) is coerced to?
Numeric
Type of object
The data structure of object. E.g. Vector, Matrix
Encapsulation
The packing of data and functions into a single component.
y <- c(1.7, "a") is coerced to?
character
Class or datatype of a vector?
class(vector)
