Overview

• Container variables store collections of data.

• Common types include vectors, lists, matrices, and data frames.

What is a Vector?

• A vector is a basic data structure that holds elements of the same type.

• Created using c() function.

# Creating a numeric vector
numeric_vector <- c(1, 2, 3, 4, 5)

Accessing Vector Elements

• Use square brackets [ ] for accessing elements.

# Accessing the third element
numeric_vector[3]

## [1] 3

What is a List?

• Lists can hold elements of different types.

• Created using list() function.

# Creating a list
mixed_list <- list("a", TRUE, 3, 1.5)

Accessing List Elements

• Use double square brackets [[ ]] for single elements.

• Use $ to access elements by name.

# Accessing the first element
mixed_list[[1]]

## [1] "a"

# Assuming the list has names
named_list <- list(name1 = "a", name2 = TRUE)
named_list$name2

## [1] TRUE

What is a Matrix?

• A matrix is a two-dimensional collection of elements of the same type.

• Created using matrix() function.

# Creating a matrix
my_matrix <- matrix(1:9, nrow = 3)

Accessing Matrix Elements

• Use [row, column] to access elements.

# Accessing element in the first row, second column
my_matrix[1, 2]

## [1] 4

What is a Data Frame?

• Data frames are used for storing tabular data.
• Columns can contain different types.
• Created using data.frame() function.

# Creating a data frame
my_data_frame <- data.frame(column1 = 1:4, column2 = c("a", "b", "c", "d"))

Accessing Data Frame Elements

• Use $ to access columns by name.
• Use [ , ] for accessing elements by row and column.

# Accessing a column
my_data_frame$column1

## [1] 1 2 3 4

# Accessing element in the first row of the second column
my_data_frame[1, "column2"]

## [1] "a"

How do you access the second element of a list named my_list?

1. my_list[2]
2. my_list[[2]]
3. my_list$2
4. my_list(2)

Answer

How do you access the third element of a numeric vector named numeric_vector?

1. numeric_vector(3)
2. numeric_vector[3]
3. numeric_vector[[3]]
4. numeric_vector$3

Answer

Given a matrix my_matrix with at least 2 rows and 2 columns, how do you access the element in the second row and first column?

1. my_matrix[2, 1]
2. my_matrix[[2, 1]]
3. my_matrix(2, 1)
4. my_matrix$2,1

Answer

How do you access the value in the first row of a column named column2 in a data frame df?

1. df[1, "column2"]
2. df[[1, "column2"]]
3. df$column2[1]
4. Both 1 and 3 are correct

Answer