Bar Plots in R

Introduction

A bar plot (or bar chart) is a graphical representation of categorical data using rectangular bars whose heights or lengths are proportional to the values they represent.

Bar plots are useful for:

• Comparing quantities
• Displaying frequencies
• Showing survey results
• Comparing sales figures
• Visualizing marks and populations

In R, bar plots are created using the barplot() function.

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Syntax

barplot(height,
        names.arg,
        main,
        xlab,
        ylab,
        col,
        horiz,
        border)

where:

• height : vector or matrix containing values.
• names.arg : labels for bars.
• main : title.
• xlab : x-axis label.
• ylab : y-axis label.
• col : color of bars.
• horiz : horizontal bar plot.
• border : border color.

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Example 1: Simple Bar Plot

Suppose sales of four products are:

Product	Sales
A	25
B	40
C	35
D	50

sales <- c(25,40,35,50)

barplot(sales)

Output:

Four bars are drawn with heights 25, 40, 35, and 50.

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Example 2: Adding Labels and Title

sales <- c(25,40,35,50)

barplot(sales,
        names.arg=c("A","B","C","D"),
        main="Product Sales",
        xlab="Products",
        ylab="Sales")

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Example 3: Changing Colors

sales <- c(25,40,35,50)

barplot(sales,
        names.arg=c("A","B","C","D"),
        col="blue")

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Different Colors

sales <- c(25,40,35,50)

barplot(sales,
        names.arg=c("A","B","C","D"),
        col=c("red","blue","green","orange"))

Each bar gets a different color.

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Example 4: Horizontal Bar Plot

sales <- c(25,40,35,50)

barplot(sales,
        names.arg=c("A","B","C","D"),
        horiz=TRUE,
        col="cyan")

horiz=TRUE produces horizontal bars.

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Example 5: Border Color

sales <- c(25,40,35,50)

barplot(sales,
        names.arg=c("A","B","C","D"),
        col="yellow",
        border="red")

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Example 6: Changing Width of Bars

sales <- c(25,40,35,50)

barplot(sales,
        width=c(1,2,1,2),
        col="green")

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Example 7: Displaying Values on Bars

sales <- c(25,40,35,50)

x <- barplot(sales,
             names.arg=c("A","B","C","D"),
             col="lightblue",ylim=c(0,60))

text(x,
     sales,
     labels=sales,
     pos=3)

text() places the values above the bars.

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Example 8: Student Marks

marks <- c(85,90,75,95,80)

barplot(marks,
        names.arg=c("John","Mary","Alex","Sara","David"),
        main="Student Marks",
        ylab="Marks",
        col="orange")

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Example 9: Population of Cities

population <- c(12,18,25,15)

barplot(population,
        names.arg=c("Delhi","Mumbai","Chennai","Kolkata"),
        col="purple",
        main="City Population")

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Example 10: Grouped Bar Plot

Suppose sales of two products over four years are:

sales <- matrix(c(
20,25,30,35,
15,20,25,30),
nrow=2,
byrow=TRUE)

barplot(sales,
        beside=TRUE,
        names.arg=c("2021","2022","2023","2024"),
        col=c("blue","red"))

legend("topleft",
       legend=c("Product A","Product B"),
       fill=c("blue","red"))

beside=TRUE places bars side-by-side.

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Example 11: Stacked Bar Plot

sales <- matrix(c(
20,25,30,35,
15,20,25,30),
nrow=2,
byrow=TRUE)

barplot(sales,
        col=c("blue","red"))

Default behavior is stacked bars.

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Example 12: Adding Grid Lines

sales <- c(25,40,35,50)

barplot(sales,
        col="lightgreen")

grid()

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Example 13: Space Between Bars

sales <- c(25,40,35,50)

barplot(sales,
        space=1.5,
        col="pink")

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Example 14: Using Data Frames

student <- data.frame(
Name=c("John","Mary","Alex","Sara"),
Marks=c(85,92,78,95)
)

barplot(student$Marks,
        names.arg=student$Name,
        col="skyblue",
        main="Student Marks")

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Example 15: Frequency Distribution

grades <- factor(c("A","B","A","C","B","A","A"))

freq <- table(grades)

barplot(freq,
        col="green",
        main="Grade Distribution")

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Important Parameters

Parameter	Purpose
height	Heights of bars
names.arg	Labels
main	Title
xlab	X-axis label
ylab	Y-axis label
col	Color
border	Border color
horiz	Horizontal bars
beside	Side-by-side bars
space	Space between bars
width	Width of bars

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Types of Bar Plots

Type	Description
Simple Bar Plot	One variable
Horizontal Bar Plot	Horizontal bars
Colored Bar Plot	Different colors
Grouped Bar Plot	Multiple categories
Stacked Bar Plot	Values stacked vertically
Frequency Bar Plot	Using table()

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Applications

• Student marks analysis
• Product sales comparison
• Population studies
• Frequency distributions
• Survey results
• Election statistics
• Department-wise employee counts
• Monthly rainfall comparison

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Difference Between Histogram and Bar Plot

Bar Plot	Histogram
Categorical data	Continuous data
Bars separated by spaces	Bars touch each other
Created using barplot()	Created using hist()
Order not important	Order important

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Conclusion

The barplot() function is one of the most widely used plotting functions in R for comparing categorical data. By changing parameters such as col, horiz, beside, and space, different styles of bar plots can be created. Grouped and stacked bar plots are especially useful for comparing multiple datasets simultaneously.