Introduction to R

How to make a comment

Put a # sign before you write the comment, r won't run it as code

create factors

create a vector that contains all the observations that belong to a limited number of categories then, factor_sex_vector <- factor(sex_vector)

construct a data frame

data.frame(name, type, diameter, rotation, rings)

Vectors

one-dimension arrays that can hold numeric data, character data (needs quotes), logical data

sorting

order() gives you the ranked position of each element when it is applied on a variable a <- c(100, 10, 1000) order(a) then you can do a[order(a)] to sort values from smallest to largest

str()

shows you the structure of your data set total # of observations, total # of variables, a full list of the variable names, data type of each variable, first observation

sum function

sum() calculates the sum of all the elements in the vector

Creating a vector

use the combine function c() my_vector <- c(12, 13, 14, 15)

Modulo

%% returns the remainder of the division of the number to the left by the number to its right

rowsums()

calculates the total for each row in the matrix

rbind

function merges matrices and/or vectors together by row matrix is ahead of vector ex: rbind(matrix 1, matrix 2, vector 1)

head() vs tail()

head()- enables you to show the first observation tail()- enables you to show the last observation

selection of data frame

like matrix selection can use vector name if you want just a specific row/column (have to put a $ in front of the vector name)

list function

list(component 1, component 2, etc)

changing the names of the levels

mainly for clarity or other reasons levels(factor_blank_vector) levels)factor_blank_vector) <- c("Female", "Male")

matrix function

matrix() 1st argument- the collection of elements that R will arrange into the row and columns of the matrix 2nd argument- byrow= indicates that the matrix is filled by the row can be true or false 3rd argument- nrow= indicates that the matrix should have n many rows ex: matrix(1:9, byrow= TRUE, nrow= 3)

Data frames

multiple data types has variables of the data set as columns and the observations as rows

Assigning variable example

my_var <- 4

nominal vs ordinal categorical variables

nominal- without an implied order ordinal- natural ordering

selecting multiple elements from a vector

poker_vector[(1, 5)] if you want a row of numbers, poker_vector[c(1:5)]

naming rows and columns of a matrix

rownames(my_matrix) <- row_names_vector colnames(my_matrix) <- col_names_vector

if you want to know if you made money on a day and want to know how much money you won on a certain day

selection_vector <- poker_vector > 0 Poker_winnings_days <- poker_vector[selection_vector]

Factors

statistical data type used to store categorical variables categorical variables is a limited number of categories

summarizing a factor

summary() give you a quick overview of the contents of the variable

ordered factors

two added levels: ordered, levels ex: factor_speed_vector <- factor(speed_vector, ordered= TRUE, c("slow", "medium", "high")

class() function

used to check the variable of the data type beforehand

comparing order pairs

Da2 <- factor_speed_vector[2] Da5 <- factor_speed_vector[5] Da2 < Da5

Selecting one or multiple elements from a matrix

Ex: my_matrix[1,3] if you select all elements of a row or column, no number is needed before or after the comma my_matrix[,1] -> selects all elements from 1st column my_matrix[1,] -> selects all elements from 1st row

cbind

function merges matrices and/or vectors together by column matrix is ahead of vector ex: cbind(matrix 1, matrix 2, vector 1)

naming parts of list

after you created the list names(my_list) <- c("name1", "name2") same time my_list <- list(name1= your_comp1, name2 = your_comp2)

lists

allows you to gather a variety of objects under one name in an ordered way can be matrices, vectors, data frames, other lists

add elements to a list

c() function Ex: ext_list <- c(my_list, my_val) 1st part- list you want the element to be added to 2nd part- element you want added to the list

selecting elements from a list

can use [[ ]] or $ Ex: shining_list[[2]][1] 1st part- selected the second component 2nd part- selected the first element

Selecting elements of a vector

can use square brackets start out at 1, not 0 poker_vector[1]

what is a matrix?

collection of elements of the same data type arranged into a number of fixed columns and rows

subset()

ex: subset(my_df, subset= some_condition) 1st argument- specifies the data set for which you want to subset 2nd argument- give R the necessary info and conditions to select the correct subset