Introduction to R Flashcards
1
Q
Assignment
A
-
2
Q
help(Syntax)
A
- Function with argument that lists all of the operators in R.
3
Q
mode()
A
- Function without argument that revels storage.
4
Q
typeof()
A
- Function without argument that reveals type of object.
- Similar to is(argument) function.
5
Q
setwd()
A
- Function without argument that changes your working directory.
6
Q
getwd()
A
- Function without argument that gets the current file path of your working directory.
7
Q
Object
A
- A storage space with an associated name.
- Everything in R is stored as an object.
8
Q
Object Naming Protocols
A
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.
9
Q
Functions
A
- A special type of R object that exist / are created to do something.
- Usually take arguments but can also have no arguments.
10
Q
Vectors
A
- 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.
11
Q
Atomic Vectors
A
- A vector containing only one data type.
12
Q
Generic Vectors (Lists)
A
- A vector that can contain more than one data type.
13
Q
Generating Vectors
A
- Can use two different functions:
1) seq()
2) c()
3) :
14
Q
:
A
- Known as the colon operator.
- Generates a sequence from:to in steps of 1.
- Can be in either increasing or decreasing order.
15
Q
seq()
A
- 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.
16
Q
c()
A
- 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.
17
Q
class(argument)
A
- Known as the class function.
- Gives the data type of the vector.
18
Q
vector1[vector2]
A
- Selects elements of vector1 whose indices are given by vector2.
- vector2 is known as the index vector.
19
Q
Matrix
A
- 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.
20
Q
Accessing Matrix Elements (Few Examples)
A
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.
21
Q
dim(argument)
A
- Known as the dimension function.
- Gives the dimension of a matrix input.
22
Q
is.matrix(argument)
A
- Gives the data type of the matrix.
23
Q
rowbind(argument)
A
- Function that assigns names to the rows, starting from row #1.
24
Q
cbind(argument)
A
- Function that assigns names to the columns, starting from column #1.
25
outer(argument, argument)
-
26
nrow(argument)
- Function that gives the number of rows of a matrix.
27
ncol(argument)
- Function that gives the numbers of columns of a matrix.
28
Properties of Lists
- 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.
29
list(argument,argument,...)
- Function that creates a list where the arguments are stored in the list elements.
- Access the elements using [[indices]] or [indices].
30
Data Frame
- 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 ([[]]).
31
class(object)
- Function that outputs the class of an object.
32
names(object)
- Function (mainly used with data frames) that outputs the names of the columns (?) data frame.
33
str(object)
- Function that gives the structure of an object.
34
head(object)
- Function that gives the first few rows of the object.
35
summary(object)
- Function that gives some statistics about an object.
36
Data Frame Extraction (Columns)
- Use a combination of extraction operators [], [[]] and $ and column names when necessary (with $).
37
install.packages("package")
- Function that finds and installs a desired function in R.
38
library(package)
- Function that calls an installed package before use.
| - Must call the package once before you can utilize their functions.
