R Matrices

A matrix is a two-dimensional data structure that can store elements of the same data type arranged in rows and columns.
Created using the matrix() function.

Example

# Creating a matrix with elements
mat1 <- matrix(c(1, 2, 3, 4, 5, 6), nrow = 2, ncol = 3, byrow = TRUE)
mat1

# Creating a matrix with a sequence
mat2 <- matrix(1:9, nrow = 3, ncol = 3)
mat2

# Creating a matrix of an collection of items
mat3 <- matrix(c("basket", "board", "tub", "glass"), nrow = 2, ncol = 2)
mat3

Accessing and Checking Elements

We can access the list with index number inside a [column_name, row_name] bracket.
And to check elements we use %in% operator.

Example

mat <- matrix(c("basket", "board", "tub", "glass"), nrow = 2, ncol = 2)
# Accessing elements by index
element <- mat[1, 2]  # Element in the first row, second column

# Accessing entire row or column
first_row <- mat[1, ]
second_column <- mat[, 2]

"basket" %in% mat

Adding and Removing of Rows and Coloums

We use cbind() and rbind() functions to add a rows and coloums respectively.
We use c() functions to remove rows and coloums in a matrix.
  1. cbind() Function - Combines a matrix coloum-wise
  2. rbind() Function - Combines a matrix row-wise

Example

vec1 <- c(1, 2, 3)
vec2 <- c("A", "B", "C")
combined_coloum_matrix <- cbind(vec1, vec2)
combined_coloum_matrix
combined_row_matrix <- rbind(vec1, vec2)
combined_row_matrix

new_matrix <- matrix(c(1, 2, 3, 4), nrow = 2, ncol = 2, byrow = TRUE)

remove_matrix <- new_matrix[-c(1), -c(1)]
remove_matrix

Matrix Operations and Functions

Functions are a built in methods that performs operations fast and easy.

Operation

Syntax

Description

Example

Addition

mat1 + mat2

Element-wise addition of two matrices.

mat_sum <- mat1 + mat2

Subraction

mat1 - mat2

Element-wise subraction of two matrices.

mat_subract <- mat1 - mat2

Multiplication

mat1 %*% mat2

Matrix multiplication.

mat_mult <- mat1 %*% t(mat2)

Element-wise Operations

mat1^2

Element-wise operations (e.g., square each element).

mat_squared <- mat1^2

Dimensions of a Matrix

dim(mat)

Returns the number of rows and columns in a matrix.

dimensions <- dim(mat)

Length of a Matrix

length(mat)

Returns the length of a matrix.

length_matrix <- length(mat)

Transposing a Matrix

t(mat)

Transposes the rows and columns of a matrix.

transposed_mat <- t(mat)

Sum of Elements in a Matrix

sum(mat)

Calculates the sum of all elements in a matrix.

mat_sum_all <- sum(mat)

Mean of Elements in a Matrix

mean(mat)

Calculates the mean (average) of elements in a matrix.

mat_mean <- mean(mat)


Example

my_list <- list(7, "eight", TRUE)
my_list

length(my_list)

element_exists <- "new_element" %in% names(my_list)
element_exists

df <- as.data.frame(my_list)
df

Quick Recap - Topics Covered

R Matrices

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