Describe Parts of a Chart in Graphical Form in R Programming – legend() Function

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: