Introduction to R

Question 1

Assignment

Answer 1

-

Question 2

help(Syntax)

Answer 2

• Function with argument that lists all of the operators in R.

Question 3

mode()

Answer 3

• Function without argument that revels storage.

Question 4

typeof()

Answer 4

• Function without argument that reveals type of object.

- Similar to is(argument) function.

Question 5

setwd()

Answer 5

• Function without argument that changes your working directory.

Question 6

getwd()

Answer 6

• Function without argument that gets the current file path of your working directory.

Question 7

Object

Answer 7

• A storage space with an associated name.

- Everything in R is stored as an object.

Question 8

Object Naming Protocols

Answer 8

1) Case sensitive names.
2) Must start with a period or letter.
- If starts with a period, a letter must follow.
3) Periods can be found anywhere in an R name but the underscore cannot start a name.
4) Names cannot have spaces.
5) Names almost never take quotes around them.

Question 9

Functions

Answer 9

• A special type of R object that exist / are created to do something.
• Usually take arguments but can also have no arguments.

Question 10

Vectors

Answer 10

• An ordered sequence in R.
• No scalars exist in R = a single value is an vector of length 1.
• [1] denotes the first element on a vector in R.
• Two types: atomic and generic vectors.

Question 11

Atomic Vectors

Answer 11

• A vector containing only one data type.

Question 12

Generic Vectors (Lists)

Answer 12

• A vector that can contain more than one data type.

Question 13

Generating Vectors

Answer 13

• Can use two different functions:
  1) seq()
  2) c()
  3) :

Question 14

:

Answer 14

• Known as the colon operator.
• Generates a sequence from:to in steps of 1.
• Can be in either increasing or decreasing order.

Question 15

seq()

Answer 15

• Known as the sequence function.
• Format of seq(from,to,by).
• Technically constructed as seq (from = a, to = b, by = c) but this is long.
• Can be in either increasing or decreasing order.

Question 16

c()

Answer 16

• Known as the concatenate function.
• Combines / concatenates values into a vector.
• Output type determined by the highest type among vector components and follows the rule: character > integer > logical.
  1) If any value is a character, the vector becomes a character vector.
  2) If no characters, and a mix of integer and logical, becomes an integer vector where logicals are converted into integers.

Question 17

class(argument)

Answer 17

• Known as the class function.

- Gives the data type of the vector.

Question 18

vector1[vector2]

Answer 18

• Selects elements of vector1 whose indices are given by vector2.
• vector2 is known as the index vector.

Question 19

Matrix

Answer 19

• An atomic vector with row and column indices.
• All rows and columns must be of the same size but can have different # of row and columns.
• Elements accessed via indexing.

Question 20

Accessing Matrix Elements (Few Examples)

Answer 20

1) objectname[r,c] = access a specific cell.
2) objectname[r,] = access all columns of a specific row.
3) objectname[,c] = access all rows of a specific column.

Question 21

dim(argument)

Answer 21

• Known as the dimension function.

- Gives the dimension of a matrix input.

Question 22

is.matrix(argument)

Answer 22

• Gives the data type of the matrix.

Question 23

rowbind(argument)

Answer 23

• Function that assigns names to the rows, starting from row #1.

Question 24

cbind(argument)

Answer 24

• Function that assigns names to the columns, starting from column #1.

Question 25

outer(argument, argument)

Answer 25

-

Question 26

nrow(argument)

Answer 26

• Function that gives the number of rows of a matrix.

Question 27

ncol(argument)

Answer 27

• Function that gives the numbers of columns of a matrix.

Question 28

Properties of Lists

Answer 28

• Can contain any type of R object.
• May have mixed elements = not atomic.
• List elements can be separated out and saved as new lists, new vectors, etc.

Question 29

list(argument,argument,…)

Answer 29

• Function that creates a list where the arguments are stored in the list elements.
• Access the elements using [[indices]] or [indices].

Question 30

Data Frame

Answer 30

• A rectangular list.
• Has “observations” in the rows and “variables” in columns in a rectangular matrix-like structure.
• row.names(put_in_names) = labels the rows.
• column.names(put_in_stuff) = labels and columns.
• Can access using matrix indexing rules ([]) or list indexing rules ([[]]).

Question 31

class(object)

Answer 31

• Function that outputs the class of an object.

Question 32

names(object)

Answer 32

• Function (mainly used with data frames) that outputs the names of the columns (?) data frame.

Question 33

str(object)

Answer 33

• Function that gives the structure of an object.

Question 34

head(object)

Answer 34

• Function that gives the first few rows of the object.

Question 35

summary(object)

Answer 35

• Function that gives some statistics about an object.

Question 36

Data Frame Extraction (Columns)

Answer 36

• Use a combination of extraction operators [], [[]] and $ and column names when necessary (with $).

Question 37

install.packages(“package”)

Answer 37

• Function that finds and installs a desired function in R.

Question 38

library(package)

Answer 38

• Function that calls an installed package before use.

- Must call the package once before you can utilize their functions.