Section 17 One Numeric: geom_histogram

The function geom_histogram maps the data to histogram.

17.1 Example 1:

data(iris)

?geom_histogram

library(ggplot2)

# geom_histogram
g <- ggplot(data=iris, mapping=aes(Sepal.Length))
g <- g + geom_histogram()
g

# bins
g <- ggplot(data=iris, mapping=aes(Sepal.Length))
g <- g + geom_histogram(bins=40)
g

# binwidth
g <- ggplot(data=iris, mapping=aes(Sepal.Length))
g <- g + geom_histogram(binwidth=0.10)
g

# fill & colour
g <- ggplot(data=iris, mapping=aes(Sepal.Length))
g <- g + geom_histogram(binwidth=0.10, fill='lightblue', colour='purple')
g

# labs
g <- ggplot(data=iris, mapping=aes(Sepal.Length))
g <- g + geom_histogram(binwidth=0.10, fill='lightblue', colour='purple')
g <- g + labs(title='Histogram of Sepal Length',
              subtitle='Based on Iris data',
              x='Sepal Length (cm)',
              y='Count')
g

# density
g <- ggplot(data=iris, mapping=aes(Sepal.Length))
g <- g + geom_histogram(mapping=aes(y=..density..),
                        binwidth=0.10, fill='lightblue', colour='purple')
g <- g + labs(title='Histogram of Sepal Length',
              subtitle='Based on Iris data',
              x='Sepal Length (cm)',
              y='Density')
g

# vline
g <- ggplot(data=iris, mapping=aes(Sepal.Length))
g <- g + geom_histogram(mapping=aes(y=..density..),
                        binwidth=0.10, fill='lightblue', colour='purple')
g <- g + geom_vline(aes(xintercept=mean(Sepal.Length, na.rm=TRUE)),   
                    colour='red', linetype='dashed', size=1.5)
g <- g + labs(title='Histogram of Sepal Length',
              subtitle='Based on Iris data',
              x='Sepal Length (cm)',
              y='Density')
g

# theme_bw()

g <- ggplot(data=iris, mapping=aes(Sepal.Length))
g <- g + geom_histogram(mapping=aes(y=..density..),
                        binwidth=0.10, fill='lightblue', colour='purple')
g <- g + geom_vline(aes(xintercept=mean(Sepal.Length, na.rm=TRUE)),   
                    colour='red', linetype='dashed', size=1.5)
g <- g + labs(title='Histogram of Sepal Length',
              subtitle='Based on Iris data',
              x='Sepal Length (cm)',
              y='Density')

g + theme_bw()

17.2 Example 2:

data(warpbreaks)

• Draw a histogram of the variable breaks

• Discuss the histogram

• Transform the data using log-transformation and redraw the histogram