Introduction to R Matrices answer

What’s a matrix?

# Construct a matrix with 3 rows that contain the numbers 1 up to 9
matrix(1:9,byrow=T,nrow=3)

Analyzing matrices, you shall

# Box office Star Wars (in millions!)
new_hope <- c(460.998, 314.4)
empire_strikes <- c(290.475, 247.900)
return_jedi <- c(309.306, 165.8)

# Create box_office
box_office <-c(new_hope, empire_strikes, return_jedi)

# Construct star_wars_matrix
star_wars_matrix <-matrix(box_office,nrow=3,byrow=T)

Naming a matrix

# Box office Star Wars (in millions!)
new_hope <- c(460.998, 314.4)
empire_strikes <- c(290.475, 247.900)
return_jedi <- c(309.306, 165.8)

# Construct matrix
star_wars_matrix <- matrix(c(new_hope, empire_strikes, return_jedi), nrow = 3, byrow = TRUE)

# Vectors region and titles, used for naming
region <- c("US", "non-US")
titles <- c("A New Hope", "The Empire Strikes Back", "Return of the Jedi")

# Name the columns with region
colnames(star_wars_matrix)<-region

# Name the rows with titles
rownames(star_wars_matrix)<-titles

# Print out star_wars_matrix
star_wars_matrix

Calculating the worldwide box office

# Construct star_wars_matrix
box_office <- c(460.998, 314.4, 290.475, 247.900, 309.306, 165.8)
star_wars_matrix <- matrix(box_office, nrow = 3, byrow = TRUE,
dimnames = list(c("A New Hope", "The Empire Strikes Back", "Return of the Jedi"),
c("US", "non-US")))

# Calculate worldwide box office figures
worldwide_vector <-rowSums(star_wars_matrix)

Adding a column for the Worldwide box office

# Construct star_wars_matrix
box_office <- c(460.998, 314.4, 290.475, 247.900, 309.306, 165.8)
star_wars_matrix <- matrix(box_office, nrow = 3, byrow = TRUE,
dimnames = list(c("A New Hope", "The Empire Strikes Back", "Return of the Jedi"),
c("US", "non-US")))

# The worldwide box office figures
worldwide_vector <- rowSums(star_wars_matrix)

# Bind the new variable worldwide_vector as a column to star_wars_matrix
all_wars_matrix <-cbind(star_wars_matrix,worldwide_vector)

Adding a row

# star_wars_matrix and star_wars_matrix2 are available in your workspace
star_wars_matrix
star_wars_matrix2

# Combine both Star Wars trilogies in one matrix
all_wars_matrix <- rbind(star_wars_matrix,star_wars_matrix2)

The total box office revenue for the entire saga

# all_wars_matrix is available in your workspace
all_wars_matrix

# Total revenue for US and non-US
total_revenue_vector <-colSums(all_wars_matrix)

# Print out total_revenue_vector
total_revenue_vector

Selection of matrix elements

# all_wars_matrix is available in your workspace
all_wars_matrix

# Select the non-US revenue for all movies
non_us_all <-all_wars_matrix[,2]

# Average non-US revenue
mean(non_us_all)

# Select the non-US revenue for first two movies
non_us_some <- all_wars_matrix[c(1,2),2]

# Average non-US revenue for first two movies
mean(non_us_some)

A little arithmetic with matrices

# all_wars_matrix is available in your workspace
all_wars_matrix

# Estimate the visitors
visitors <-all_wars_matrix/5

# Print the estimate to the console
visitors

A little arithmetic with matrices (2)

# all_wars_matrix and ticket_prices_matrix are available in your workspace
all_wars_matrix
ticket_prices_matrix

# Estimated number of visitors
visitors <-all_wars_matrix/ticket_prices_matrix

# US visitors
us_visitors <-visitors[,1]

# Average number of US visitors
print(mean(us_visitors))