Lists, why would you need them?

• Vectors: one dimensional array
  • can hold numerix, character, or logical values, the elements in a vector all have the same data type
• Matrices: two dimensional array
  • can hold numeric, charterm or logical values. The elements in a matrix all have the same data type
• Data frames: two dimensional objects
  • can hold numeric charter or logical values. Within a column all elements have the same data type, buy different columns can be of different data type.

Lists, why would you need them? (2)

• lists

Create List

# Vector with numerics from 1 up to 10
my_vector <- 1:10 
# Matrix with numerics from 1 up to 9
my_matrix <- matrix(1:9, ncol = 3)
# First 10 elements of the built-in data frame mtcars
my_df <- mtcars[1:10,]
# Construct list with these different elements:
my_list <-list(my_vector, my_matrix, my_df)

Creating a names list

# The variables mov, act and rev are available
# Finish the code to build shining_list
shining_list <- list(moviename = mov, actors = act, reviews = rev)
# The variables mov, act and rev are available
# Finish the code to build shining_list
shining_list <- list(moviename = mov, actors = act, reviews = rev)

Selecting elements from a lit

shining_list[["reviews"]]
shining_list$reviews

# shining_list is already pre-loaded in the workspace
# Print out the vector representing the actors
shining_list$actors
[1] "Jack Nicholson"   "Shelley Duvall"   "Danny Lloyd"      "Scatman Crothers"
[5] "Barry Nelson"    
# Print the second element of the vector representing the actors
shining_list$actors[[2]]
[1] "Shelley Duvall"

creating a new list for another movie

# Use the table from the exercise to define the comments and scores vectors
scores <- c(4.6, 5, 4.8, 5, 4.2)
comments <- c("I would watch it again", "Amazing!", "I liked it", "One of the best movies", "Fascinating plot")

# Save the average of the scores vector as avg_review
avg_review <- mean(scores)

# Combine scores and comments into the reviews_df data frame
reviews_df <- data.frame(scores, comments)

# Create and print out a list, called departed_list
departed_list <- list(movie_title, movie_actors, reviews_df, avg_review)
departed_list