Introduction to R Matrices answer

What’s a matrix?

# Construct a matrix with 3 rows that contain the numbers 1 up to 9matrix(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_officebox_office <-c(new_hope, empire_strikes, return_jedi) # Construct star_wars_matrixstar_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 matrixstar_wars_matrix <- matrix(c(new_hope, empire_strikes, return_jedi), nrow = 3, byrow = TRUE)# Vectors region and titles, used for namingregion <- c("US", "non-US")titles <- c("A New Hope", "The Empire Strikes Back", "Return of the Jedi")# Name the columns with regioncolnames(star_wars_matrix)<-region# Name the rows with titlesrownames(star_wars_matrix)<-titles# Print out star_wars_matrixstar_wars_matrix

Calculating the worldwide box office

# Construct star_wars_matrixbox_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 figuresworldwide_vector <-rowSums(star_wars_matrix) 

Adding a column for the Worldwide box office

# Construct star_wars_matrixbox_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 figuresworldwide_vector <- rowSums(star_wars_matrix)# Bind the new variable worldwide_vector as a column to star_wars_matrixall_wars_matrix <-cbind(star_wars_matrix,worldwide_vector) 

Adding a row

# star_wars_matrix and star_wars_matrix2 are available in your workspacestar_wars_matrix  star_wars_matrix2 # Combine both Star Wars trilogies in one matrixall_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 workspaceall_wars_matrix# Total revenue for US and non-UStotal_revenue_vector <-colSums(all_wars_matrix) # Print out total_revenue_vectortotal_revenue_vector

Selection of matrix elements

# all_wars_matrix is available in your workspaceall_wars_matrix# Select the non-US revenue for all moviesnon_us_all <-all_wars_matrix[,2]# Average non-US revenuemean(non_us_all)# Select the non-US revenue for first two moviesnon_us_some <- all_wars_matrix[c(1,2),2]# Average non-US revenue for first two moviesmean(non_us_some)

A little arithmetic with matrices

# all_wars_matrix is available in your workspaceall_wars_matrix# Estimate the visitorsvisitors <-all_wars_matrix/5 # Print the estimate to the consolevisitors

A little arithmetic with matrices (2)

# all_wars_matrix and ticket_prices_matrix are available in your workspaceall_wars_matrixticket_prices_matrix# Estimated number of visitorsvisitors <-all_wars_matrix/ticket_prices_matrix# US visitorsus_visitors <-visitors[,1] # Average number of US visitorsprint(mean(us_visitors))