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setdiff() Function in detail

The setdiff() function in R is used to find elements that are present in the first object but not in the second object.

Syntax:

setdiff(x, y)

Parameters:

• x and y: Objects containing a sequence of items.

Example 1: Using setdiff() with Numeric Vectors

# R program to illustrate setdiff() function

# Vector 1
num_vec1 <- c(10, 20, 30, 40, 50, 60, 50, 50)

# Vector 2
num_vec2 <- c(20:40)

# Calling setdiff() function
result <- setdiff(num_vec1, num_vec2)

print(result)

Output:

[1] 10 50 60

Example 2: Using setdiff() with Character Vectors

# R program to illustrate setdiff() function

# Vector 1
char_vec1 <- c("Apple", "Orange")

# Vector 2
char_vec2 <- c("Apple", "Banana", "Mango")

# Calling setdiff() function
result <- setdiff(char_vec1, char_vec2)

print(result)

Output:

[1] "Orange"

Example 3: Using setdiff() with Data Frames

# R program to illustrate setdiff() function

# Data frame 1
df1 <- data.frame(A = c(15, 25, 35),
                  B = c(5, 5, 5))

# Data frame 2
df2 <- data.frame(C = c(5, 10, 15),
                  D = c(5, 5, 5))

# Calling setdiff() function
result <- setdiff(df1, df2)

print(result)

Output:

A
1 15
2 25
3 35

Outer() Function in detail

A flexible tool for working with matrices and vectors in R is the outer() function. It enables you to create a new matrix or array by applying a function to every possible combination of the elements from two input vectors. The outer() function in R is used to apply a function to two arrays.

Syntax:

outer(X, Y, FUN = "*")

Parameters:

• x, y: Arrays
• FUN: Function to use on the outer products, default value is multiplication (*)

The outer() function in R produces a matrix or array with dimensions corresponding to the outer product of X and Y. The function FUN is applied to the respective pair of elements from X and Y to generate each element of the result.

Examples

Example 1: Outer Product of Two Vectors

# Initializing two arrays of elements
x <- c(2, 4, 6, 8, 10)
y <- c(3, 6, 9)

# Multiplying elements of x with elements of y
outer(x, y)

Output:

[,1] [,2] [,3]
[1,]    6   12   18
[2,]   12   24   36
[3,]   18   36   54
[4,]   24   48   72
[5,]   30   60   90

Example 2: Outer Function for a Vector and a Single Value

# Initializing a vector and a single value
a <- 1:7
b <- 5

# Adding elements of a with b
outer(a, b, "+")

Output:

[,1]
[1,]    6
[2,]    7
[3,]    8
[4,]    9
[5,]   10
[6,]   11
[7,]   12

Types of outer() Functions

Since the outer() function is general, you can define custom functions and use them with outer(). Below are some commonly used types:

1. Arithmetic Functions

The most common use of outer() is for performing arithmetic operations such as addition, subtraction, multiplication, and division on two vectors. The operators +, -, *, /, %%, and %/% can be applied.

Example:

x <- 2:4
y <- 5:7
outer(x, y, FUN = "-")

Output:

[,1] [,2] [,3]
[1,]   -3   -4   -5
[2,]   -2   -3   -4
[3,]   -1   -2   -3

2. Statistical Functions

Statistical operations can also be applied using outer(). For example, suppose we want to find the product of two matrices.

Example:

# Creating two matrices
A <- matrix(2:7, nrow = 2, ncol = 3)
B <- matrix(1:4, nrow = 2, ncol = 2)

# Multiplying the two matrices using the outer function
outer(A, B, "*")

Output:

, , 1, 1

     [,1] [,2] [,3]
[1,]    2    4    6
[2,]    3    5    7

, , 2, 1

     [,1] [,2] [,3]
[1,]    4    8   12
[2,]    6   10   14

, , 1, 2

     [,1] [,2] [,3]
[1,]    6   12   18
[2,]    9   15   21

, , 2, 2

     [,1] [,2] [,3]
[1,]    8   16   24
[2,]   12   20   28

as.logical() Function in details

The as.logical() function in R is used to convert an object to a logical vector.

Syntax:

as.logical(x)

Parameters:

• x: Numeric or character object.

Example 1: Basic Example of as.logical() Function in R

# R Program to convert an object to a logical vector

# Creating a vector
x <- c(0, 1, 2, -3, 4, NA)

# Calling as.logical() function
print(as.logical(1))
print(as.logical("FALSE"))
print(as.logical(0))
print(as.logical(x))

Output:

[1] TRUE
[1] FALSE
[1] FALSE
[1] FALSE  TRUE  TRUE  TRUE  TRUE    NA

Example 2: Converting Matrices with as.logical() Function in R

# R Program to convert matrices to logical vectors

# Creating matrices
matrix1 <- matrix(c(0, 1, 3, 4), 2, 2)
matrix2 <- matrix(c(0, 0, 1, -1), 2, 2)

# Calling as.logical() function
print(as.logical(matrix1))
print(as.logical(matrix2))

Output:

[1] FALSE  TRUE  TRUE  TRUE
[1] FALSE FALSE  TRUE  TRUE

Sorting of Arrays in details

A vector is a one-dimensional array, defined by a single length dimension. A vector can be created using the c() function by passing a list of values. Sorting can be done in either ascending or descending order. Before sorting, certain factors should be considered:

• Sorting order – Ascending or Descending.
• Sorting based on multiple criteria – If sorting involves multiple columns, specify the order.
• Handling missing and duplicate values – Decide whether to remove or replace them, considering the impact on the data.

Method 1: sort() function

The sort() function in R is used to sort a vector. By default, it sorts in increasing order. To sort in descending order, set the decreasing parameter to TRUE.

Syntax:

sort(vector_name, decreasing = TRUE)

Parameters:

• vector_name: The vector to be sorted.
• decreasing: A Boolean value that determines whether sorting should be in descending order.

Example 1: Sorting in Ascending Order

# Create a vector
numbers <- c(45, 12, 78, 23, 56, 89, 34)

# Sort in ascending order
sort(numbers)

Output:

[1] 12 23 34 45 56 78 89

Example 2: Sorting in Descending Order

# Sort in descending order
sort(numbers, decreasing = TRUE)

Output:

[1] 89 78 56 45 34 23 12

Method 2: order() function

To sort data frames, the order() function is used. It sorts the data based on the specified column. To sort in descending order, use a negative sign. Sorting can also be done with multiple criteria. If two values in a column are the same, a secondary column can be used for sorting (e.g., sorting names alphabetically when ages are the same).

Example: Sorting a Data Frame by Age

# Define a data frame
students <- data.frame("Age" = c(20, 18, 22, 25, 19),
                       "Name" = c("Aria", "Leo", "Sophia", "Daniel", "Mia"))

# Sort the data frame based on the Age column
sorted_students <- students[order(students$Age), ]

# Print the sorted data frame
print(sorted_students)

Output:

Age    Name
2  18    Leo
5  19    Mia
1  20    Aria
3  22    Sophia
4  25    Daniel

Example 1: Sorting a Vector in Decreasing Order

# Define vector
numbers <- c(35, 10, 50, 25, 5, 40)

# Sort in decreasing order and return indices
order(-numbers)

Output:

[1] 3 6 1 4 2 5

Example 2: Sorting a Data Frame by Multiple Columns

# Define dataframe
students <- data.frame("Age" = c(14, 18, 14, 21, 18, 14),
                       "Name" = c("Liam", "Emma", "Noah",
                                  "Olivia", "Ava", "Sophia"))

# Sort the dataframe first by Age, then by Name
sorted_students <- students[order(students$Age, students$Name), ]

# Print sorted dataframe
print(sorted_students)

Output:

Age    Name
6   14  Sophia
3   14   Noah
1   14   Liam
5   18     Ava
2   18   Emma
4   21 Olivia

Method 3: Sorting an Array Using a Loop

# Create linear array
arr <- c(8, 3, 7, 2, 6, 5, 4, 1)

# Repeat until the array is sorted
repeat
{
    swapped <- FALSE

    # Iterate through the array
    for (i in 2:length(arr))
    {
        newArr <- arr
        if (arr[i - 1] > arr[i])
        {
            newArr[i - 1] <- arr[i]
            newArr[i] <- arr[i - 1]
            arr <- newArr
            swapped <- TRUE
        }
    }

    if (!swapped) {break}
}

# Print sorted array
print(arr)

Output:

[1] 1 2 3 4 5 6 7 8

Method 4: Using dplyr Package for Sorting

# Install and load dplyr package
install.packages("dplyr")
library(dplyr)

# Create dataframe
employees <- data.frame("Age" = c(30, 45, 28, 35, 40),
                        "Name" = c("David", "Alice", "Ethan",
                                   "Olivia", "Sophia"))

# Sort the dataframe by Age using arrange()
sorted_employees <- arrange(employees, Age)

# Print sorted dataframe
print(sorted_employees)

Output:

Age    Name
3   28   Ethan
1   30   David
4   35  Olivia
5   40  Sophia
2   45   Alice

Array Operations in detail

Arrays are R data objects that store data in more than two dimensions. Arrays are n-dimensional data structures. For example, if we create an array of dimensions (2, 3, 3), it creates three rectangular matrices, each with two rows and three columns. They are homogeneous data structures.

To create an array in R, use the function array(). The arguments to this function include a set of elements in vectors and a vector containing the dimensions of the array.

Syntax:

Array_NAME <- array(data, dim = (row_Size, column_Size, matrices, dimnames))

where:

• data – An input vector given to the array.
• matrices – Consists of multi-dimensional matrices.
• row_Size – Number of row elements that an array can store.
• column_Size – Number of column elements that an array can store.
• dimnames – Used to change the default names of rows and columns according to user preference.

Example:

# Create the vectors with different lengths
vector1 <- c(5, 7, 9)
vector2 <- c(12, 14, 16, 18, 20, 22)

# Creating an array using these vectors
result <- array(c(vector1, vector2), dim = c(3, 3, 2))
print(result)

Naming Columns and Rows

We can assign names to the rows and columns using dimnames.

Example:

# Creating Vectors
vector1 <- c(2, 4, 6)
vector2 <- c(8, 10, 12, 14, 16, 18)

# Assigning Names to rows and columns
column.names <- c("A", "B", "C")
row.names <- c("X", "Y", "Z")
matrix.names <- c("Table1", "Table2")

# Creating an array with named dimensions
result <- array(c(vector1, vector2), dim = c(3, 3, 2),
                dimnames = list(row.names, column.names, matrix.names))
print(result)

Output:

, , 1

     [,1] [,2] [,3]
[1,]    5   12   18
[2,]    7   14   20
[3,]    9   16   22

, , 2

     [,1] [,2] [,3]
[1,]    5   12   18
[2,]    7   14   20
[3,]    9   16   22

Manipulating Array Elements

An array consists of multiple dimensions, and operations can be performed by accessing elements.

Example:

# Creating vectors
vector1 <- c(3, 6, 9)
vector2 <- c(2, 4, 6, 8, 10, 12)
array1 <- array(c(vector1, vector2), dim = c(3, 3, 2))

# Creating another array
vector3 <- c(1, 3, 5)
vector4 <- c(7, 9, 11, 13, 15, 17)
array2 <- array(c(vector3, vector4), dim = c(3, 3, 2))

# Extracting matrices and adding them
matrix1 <- array1[,,2]
matrix2 <- array2[,,2]
result <- matrix1 + matrix2
print(result)

Output:

[,1] [,2] [,3]
[1,]    9   13   17
[2,]   11   15   19
[3,]   13   19   23

Accessing Array Elements in R

Using index positions in a matrix, any element can be accessed easily. Additionally, elements in an array can be modified using index positions.

Syntax:

Array_Name[row_position, Column_Position, Matrix_Level]

Example:

# Creating Vectors
vector1 <- c(5, 8, 2)
vector2 <- c(14, 7, 9, 6, 11, 3)

# Defining names
column.names <- c("Col1", "Col2", "Col3")
row.names <- c("Row1", "Row2", "Row3")
matrix.names <- c("Matrix1", "Matrix2")

# Creating an array
result <- array(c(vector1, vector2), dim = c(3, 3, 2),
                dimnames = list(row.names, column.names, matrix.names))

print(result)

# Print second row of first matrix
print(result[2,,1])

Output:

, , Matrix1

     Col1 Col2 Col3
Row1    5   14    6
Row2    8    7   11
Row3    2    9    3

, , Matrix2

     Col1 Col2 Col3
Row1    5   14    6
Row2    8    7   11
Row3    2    9    3

Col1 Col2 Col3
   8    7   11

Performing Calculations Across Array Elements

The apply() function is used for performing calculations on array elements.

Syntax:

apply(x, margin, fun)

• x – an array.
• margin – dimension specification (1 for rows, 2 for columns).
• fun – function to be applied to the elements of the array.

Example:

# Creating vectors
vector1 <- c(4, 3, 7)
vector2 <- c(1, 5, 6, 9, 2, 8)

# Creating an array
new_array <- array(c(vector1, vector2), dim = c(3, 3, 2))

print(new_array)

# Calculate sum of columns in matrices
result <- apply(new_array, c(2), sum)

print(result)

Output:

, , 1

     [,1] [,2] [,3]
[1,]    4    1    9
[2,]    3    5    2
[3,]    7    6    8

, , 2

     [,1] [,2] [,3]
[1,]    4    1    9
[2,]    3    5    2
[3,]    7    6    8

[1] 28 24 38

Multidimensional Array in detail

Arrays in R are data objects that store data in more than two dimensions. For example, if we create an array of dimensions (2, 3, 4), it forms 4 rectangular matrices, each containing 2 rows and 3 columns. These types of arrays are called Multidimensional Arrays.

Creating a Multidimensional Array

An array is created using the array() function. It takes vectors as input and uses the values in the dim parameter to define the number of dimensions.

Syntax:

grep(pattern, text_vector, ignore.case=FALSE)MArray = array(c(vec1, vec2), dim)

Example:

# Create two vectors
vector1 <- c(2, 4, 6)
vector2 <- c(8, 10, 12, 14, 16, 18)

# Create an array from these vectors
result <- array(c(vector1, vector2), dim = c(3, 3, 2))

# Print the array
print(result)

Output:

, , 1

     [,1] [,2] [,3]
[1,]    2    8   14
[2,]    4   10   16
[3,]    6   12   18

, , 2

     [,1] [,2] [,3]
[1,]    2    8   14
[2,]    4   10   16
[3,]    6   12   18

Naming Columns and Rows

We can assign names to rows, columns, and matrices in the array using the dimnames parameter.

Example:

# Create two vectors
vector1 <- c(2, 4, 6)
vector2 <- c(8, 10, 12, 14, 16, 18)

# Define names for rows, columns, and matrices
column.names <- c("Col_A", "Col_B", "Col_C")
row.names <- c("Row_1", "Row_2", "Row_3")
matrix.names <- c("Matrix_A", "Matrix_B")

# Create an array with names
result <- array(c(vector1, vector2), dim = c(3, 3, 2),
                dimnames = list(row.names, column.names, matrix.names))

# Print the array
print(result)

Output:

, , Matrix_A

       Col_A Col_B Col_C
Row_1     2     8    14
Row_2     4    10    16
Row_3     6    12    18

, , Matrix_B

       Col_A Col_B Col_C
Row_1     2     8    14
Row_2     4    10    16
Row_3     6    12    18

Manipulating Array Elements

Since arrays consist of matrices in multiple dimensions, operations can be performed by accessing individual matrix elements.

Example:

# Create first array
vector1 <- c(2, 4, 6)
vector2 <- c(8, 10, 12, 14, 16, 18)
array1 <- array(c(vector1, vector2), dim = c(3, 3, 2))

# Create second array
vector3 <- c(1, 3, 5)
vector4 <- c(7, 9, 11, 13, 15, 17)
array2 <- array(c(vector3, vector4), dim = c(3, 3, 2))

# Extract second matrices from both arrays
matrix1 <- array1[,,2]
matrix2 <- array2[,,2]

# Add the matrices
result <- matrix1 + matrix2
print(result)

Output:

[,1] [,2] [,3]
[1,]    9   21   27
[2,]   17   25   31
[3,]   23   33   35

R – Array

Arrays are fundamental data storage structures defined with a specific number of dimensions. They are used to allocate space in contiguous memory locations.

In R Programming, one-dimensional arrays are called vectors, where their single dimension is their length. Two-dimensional arrays are referred to as matrices, which consist of a defined number of rows and columns. Arrays in R hold elements of the same data type. Vectors serve as inputs to create arrays, specifying their dimensions.

Creating an Array

In R, arrays can be created using the array() function. The function takes a list of elements and dimensions as inputs to create the desired array.

Syntax:

array(data, dim = c(nrow, ncol, nmat), dimnames = names)

Components:

• nrow: Number of rows.
• ncol: Number of columns.
• nmat: Number of matrices with dimensions nrow * ncol.
• dimnames: Defaults to NULL. Alternatively, a list can be provided containing names for each component of the array dimensions.

Uni-Dimensional Array

A vector, a one-dimensional array, has its length as its dimension. It can be created using the c() function.

Example:

vec <- c(10, 20, 30, 40, 50)
print(vec)

# Displaying the length of the vector
cat("Length of the vector: ", length(vec))

Output:

[1] 10 20 30 40 50
Length of the vector:  5

Multi-Dimensional Array

A matrix, or a two-dimensional array, is defined by rows and columns of the same data type. Matrices are created using the array() function.

Example:

# Create a matrix with values from 15 to 26
mat <- array(15:26, dim = c(2, 3, 2))
print(mat)

Output:

, , 1
     [,1] [,2] [,3]
[1,]   15   17   19
[2,]   16   18   20

, , 2
     [,1] [,2] [,3]
[1,]   21   23   25
[2,]   22   24   26

Naming Array Dimensions

You can assign names to rows, columns, and matrices using vectors for better readability.

Example:

rows <- c("Row1", "Row2")
columns <- c("Col1", "Col2", "Col3")
matrices <- c("Matrix1", "Matrix2")

named_array <- array(1:12, dim = c(2, 3, 2),
                     dimnames = list(rows, columns, matrices))
print(named_array)

Output:

, , Matrix1
     Col1 Col2 Col3
Row1    1    3    5
Row2    2    4    6

, , Matrix2
     Col1 Col2 Col3
Row1    7    9   11
Row2    8   10   12

Accessing Arrays

You can access elements of arrays using indices for each dimension. Names or positions can be used.

Example:

vec <- c(5, 10, 15, 20, 25)
cat("Vector:", vec)
cat("Second element:", vec[2])

Output:

Vector: 5 10 15 20 25
Second element: 10

Accessing Matrices in an Array

Example:

rows <- c("A", "B")
columns <- c("X", "Y", "Z")
matrices <- c("M1", "M2")

multi_array <- array(1:12, dim = c(2, 3, 2),
                     dimnames = list(rows, columns, matrices))

# Accessing first matrix
print("Matrix M1")
print(multi_array[, , "M1"])

# Accessing second matrix by index
print("Matrix 2")
print(multi_array[, , 2])

Output:

Matrix M1
     X Y Z
A    1 3 5
B    2 4 6

Matrix 2
     X Y Z
A    7 9 11
B    8 10 12

Accessing Specific Rows and Columns

Example:

print("First row of Matrix 1")
print(multi_array[1, , "M1"])

print("Second column of Matrix 2")
print(multi_array[, 2, 2])

Output:

First row of Matrix 1
X Y Z
1 3 5

Second column of Matrix 2
A 9
B 10

Modifying Arrays

Adding Elements to Arrays: New elements can be added at specific positions or appended to the array.

Example:

vec <- c(1, 2, 3, 4)

# Adding an element using c()
vec <- c(vec, 5)
print("After appending an element:")
print(vec)

# Using append() to add after the 2nd element
vec <- append(vec, 10, after = 2)
print("After using append:")
print(vec)

Output:

After appending an element:
[1] 1 2 3 4 5

After using append:
[1]  1  2 10  3  4  5

Removing Elements

Elements can be removed using logical conditions or indices.

Example:

vec <- c(1, 2, 3, 4, 5, 6)
vec <- vec[vec != 4]  # Removing element with value 4
print(vec)

Output:

[1] 1 2 3 5 6

Principal Component Analysis in detail

Principal Component Analysis (PCA) is a technique used to analyze the linear components of all existing attributes in a dataset. Principal components are linear combinations (orthogonal transformations) of the original predictors in the dataset. PCA is widely used in Exploratory Data Analysis (EDA) as it helps in visualizing the variations present in high-dimensional data.

Understanding PCA

The first principal component captures the maximum variance in the dataset and determines the direction of the highest variability. The second principal component captures the remaining variance while being uncorrelated with the first component (PC1). This pattern continues with all succeeding principal components, ensuring that they capture the remaining variance without correlation with previous components.

Dataset

We will use the iris dataset, which is built into R. It contains measurements of sepal length, sepal width, petal length, and petal width for three different species of flowers.

Installing Required Packages

legend(x, y, legend, fill, col, bg, lty, cex, title, text.font)

Loading the Package and Dataset

library(dplyr)
data(iris)
str(iris)

Output:

' data.frame': 150 obs. of  5 variables:
$ Sepal.Length: num  5.1 4.9 4.7 4.6 5 ...
$ Sepal.Width : num  3.5 3 3.2 3.1 3.6 ...
$ Petal.Length: num  1.4 1.4 1.3 1.5 1.4 ...
$ Petal.Width : num  0.2 0.2 0.2 0.2 0.2 ...
$ Species     : Factor w/ 3 levels "setosa","versicolor", "virginica" ...

Principal Component Analysis with R language using dataset

We perform Principal Component Analysis (PCA) on the mtcars dataset, which includes 32 car models and 10 variables.

# Load dataset
data(iris)

# Remove non-numeric column
iris_numeric <- iris[, -5]

# Apply PCA using prcomp function
my_pca <- prcomp(iris_numeric, scale = TRUE, center = TRUE, retx = TRUE)

# View summary
summary(my_pca)

# View principal component loadings
my_pca$rotation

# View transformed principal components
dim(my_pca$x)
my_pca$x

# Plot the resultant principal components
biplot(my_pca, main = "Biplot", scale = 0)

# Compute variance and proportion of variance explained
my_pca.var <- my_pca$sdev^2
propve <- my_pca.var / sum(my_pca.var)

# Scree plot
plot(propve, xlab = "Principal Component",
     ylab = "Proportion of Variance Explained",
     ylim = c(0, 1), type = "b", main = "Scree Plot")

# Cumulative variance plot
plot(cumsum(propve),
     xlab = "Principal Component",
     ylab = "Cumulative Proportion of Variance Explained",
     ylim = c(0, 1), type = "b")

# Find the number of components covering at least 90% variance
which(cumsum(propve) >= 0.9)[1]

# Prepare data for Decision Tree
train.data <- data.frame(Sepal.Length = iris$Sepal.Length, my_pca$x[, 1:4])

# Install and load decision tree packages
install.packages("rpart")
install.packages("rpart.plot")
library(rpart)
library(rpart.plot)

# Build Decision Tree model
rpart.model <- rpart(Sepal.Length ~ ., data = train.data, method = "anova")

# Plot the Decision Tree
rpart.plot(rpart.model)

Output:

Variance explained for each principal component

Cumulative proportion of variance

Decision tree model

legend() Function in detail

The legend() function in R is used to add legends to an existing plot. A legend is an area within the graph plot that describes the elements of the plot. The legend helps visualize statistical data effectively.

Syntax:

legend(x, y, legend, fill, col, bg, lty, cex, title, text.font)

Parameters:

• x and y: Coordinates used to position the legend.
• legend: Text for the legend.
• fill: Colors used for filling the boxes in the legend.
• col: Colors of lines.
• bg: Background color for the legend box.
• title: Optional title for the legend.
• text.font: Integer specifying the font style of the legend (optional).

Returns:

A legend added to the plot.

Example 1: Basic Usage of legend()

# Generate some data
x <- 1:10
y1 <- x * x
y2 <- 2 * y1

# Create a plot with two lines
plot(x, y1, type = "b", pch = 19, col = "blue", xlab = "X", ylab = "Y")
lines(x, y2, pch = 22, col = "red", type = "b", lty = 6)

# Add a basic legend
legend("topright", legend = c("Line A", "Line B"), col = c("blue", "red"), lty = 1:2)

Output:

Example 2: Adding Title, Font, and Background Color to Legend

makePlot <- function(){
  x <- 1:10
  y1 <- x * x
  y2 <- 2 * y1
  plot(x, y1, type = "b", pch = 19, col = "blue", xlab = "X", ylab = "Y")
  lines(x, y2, pch = 22, col = "red", type = "b", lty = 6)
}
makePlot()

# Add a legend with customization
legend(1, 95, legend = c("Curve A", "Curve B"), col = c("blue", "red"), lty = 1:2, cex = 0.9,
       title = "Graph Types", text.font = 6, bg = "lightgray")

Output:

Example 3: Modifying Legend Box Border

makePlot <- function(){
  x <- 1:10
  y1 <- x * x
  y2 <- 2 * y1
  plot(x, y1, type = "b", pch = 22, col = "blue", xlab = "X", ylab = "Y")
  lines(x, y2, pch = 18, col = "red", type = "b", lty = 4)
}

# Change the border of the legend
makePlot()
legend(1, 100, legend = c("Curve A", "Curve B"), col = c("blue", "red"), lty = 1:2, cex = 0.8,
       box.lty = 4, box.lwd = 2, box.col = "blue")

Output:

Example 4: Removing the Legend Border

makePlot <- function(){
  x <- 1:10
  y1 <- x * x
  y2 <- 2 * y1
  plot(x, y1, type = "b", pch = 22, col = "blue", xlab = "X", ylab = "Y")
  lines(x, y2, pch = 18, col = "red", type = "b", lty = 4)
}

# Remove legend border using box.lty = 0
makePlot()
legend(2, 100, legend = c("Curve A", "Curve B"), col = c("blue", "red"), lty = 1:2, cex = 0.8, box.lty = 0)

Output:

Example 5: Creating a Horizontal Legend with Different Symbols

makePlot()

# Add a horizontal legend with different symbols
legend("bottom", legend = c("Curve A", "Curve B"), col = c("blue", "red"), lty = 1:2, pch = c(19, 22), horiz = TRUE)

Output: