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What are bar plots in R programming?

AKASH BAJWA

A bar plot displays data in rectangular bars, with the lengths of the bars proportional to the value of the variable. R uses the barplot() subroutine to generate bar plots. R generates both types of bar plots, vertical and horizontal. You can pass different arguments to customize the barplot() function.

Syntax

The prototype of the barplot() function is as follows:

barplot(h, xlab, ylab, main, names.arg, col)

Parameters

The barplot() function accepts the following parameters:

  • h: a matrix that contains numeric values of the chart
  • xlab: a tag for the x-axis
  • ylab: a tag for the y-axis
  • main: the title for bar plot
  • names.arg: a vector of labels that appear in each bar
  • col: specifies the colors of the bars

Examples

Bar plot without title or tags

The code below plots a simple bar plot. We pass the data vector as an argument to the barplot() method to generate a graph.

# Create the data for the chart
data <- c(8,13,26,3,43,21)

# Give the chart file a name
png(file = "barplot.png")

# Plot the bar chart 
barplot(data)

Bar plot with title and tags

In this example, the bar plot contains x and y labels, as well as a graph name. The code below plots a graph that represents the population of different states in the United States.

# Create the data 
data <- c(8,13,26,3,43,21)
labels <- c("Calif.", "Colo.", "Wash.", "Fla.", "Ga.", "Tex.")
# Plot 
barplot(data, xlab= "States", ylab = "Population in 1000s", main="Population Chart",names.arg = labels, col ="red", border = "yellow")
# Give a name to file
png(file = "US_States.png")

Note: The png(file = "US_States.png") command saves the bar plot as a file named US_States.png.

Types of bar plots in R

R programming offers multiple types of bar plots, such as:

  1. Simple colored bar plot
  2. Horizontal bar plot
  3. Bar plot with labels
  4. Stacked bar plot with legend
  5. Grouped bar plot with legend

1. Simple colored bar plot

The code below plots a simple bar plot. We pass the data vector as an argument to the barplot() method to generate a blue graph.

# Create data 
data <- c(0.2, 0.75, 0.2, 0.4, 0.5)
barplot(data, col = "#3375FF")
# Give a name to file
png(file = "graph.png")

2. Horizontal bar plot

To plot the graph horizontally, the horiz parameter must be set to TRUE, as shown below:

# Horizontal barplots
data <- c(0.2, 0.65, 0.3, 0.4, 0.5)
barplot(data, horiz = TRUE)
# Give a name to file
png(file = "graph.png")

3. Bar plot with labels

Each bar can also be given a specific name or label by setting the names.arg attribute equal to the desired bar labels, e.g., labels <- LETTERS[1:6].

The LETTERS[1:6] command generates English letters from A to F, as shown below:

# Create grouping variable
data <- c(0.2, 0.65, 0.3, 0.4, 0.5,0.8)
labels <- LETTERS[1:6]
# Add labels
barplot(data, names.arg =labels)
# Give a name to file
png(file = "graph.png")

4. Stacked bar plot with a legend

To generate a stacked bar plot with a legend, you can use the legend() method with specific parameters, as shown below:

# Create matrix for stacked barplot
data <- as.matrix(data.frame(A = c(0.9, 1.2), B = c(0.6, 0.3), C = c(0.6, 0.3), D = c(0.4, 0.4), E = c(0.3, 0.1), F = c(0.3, 0.1)))
# Create stacked barplot
barplot(data, col = c("#3375FF", "#494B4F"))
# Add legend 
legend("topright", legend = c("Covid Patients", "Pneumonia Patients"), fill = c("#3375FF", "#494B4F"))
# Give a name to file
png(file = "graph.png")

5. Grouped bar plot with a legend

Grouped bar plots can be used to compare multiple instances together. The code below compares 55 rounds of soccer matches between Bolivia and Paraguay.

data <- as.matrix(data.frame(R1 = c(0.9, 1.2), R2 = c(0.6, 0.3), R3 = c(0.6, 0.3), R4 = c(0.4, 0.4), R5 = c(0.3, 0.1)))
# Create grouped barplot
barplot(data,  col = c("#FF3333", "#3375FF"), beside = TRUE)
# Add legend 
legend("topright", legend = c("Bolivia", "Paraguay"), fill = c("#FF3333", "#3375FF"))
# Give a name to file
png(file = "graph.png")

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