# Histogram

A histogram consists of parallel vertical bars that graphically shows the frequency distribution of a quantitative variable. The area of each bar is equal to the frequency of items found in each class.

#### Example

In the data set faithful, the histogram of the eruptions variable is a collection of parallel vertical bars showing the number of eruptions classified according to their durations.

#### Problem

Find the histogram of the eruption durations in faithful.

#### Solution

We apply the hist function to produce the histogram of the eruptions variable.

> duration = faithful\$eruptions
> hist(duration,    # apply the hist function
+   right=FALSE)    # intervals closed on the left

The histogram of the eruption durations is:

#### Enhanced Solution

To colorize the histogram, we select a color palette and set it in the col argument of hist. In addition, we update the titles for readability.

> colors = c("red", "yellow", "green", "violet", "orange",
+   "blue", "pink", "cyan")
> hist(duration,    # apply the hist function
+   right=FALSE,    # intervals closed on the left
+   col=colors,     # set the color palette
+   main="Old Faithful Eruptions", # the main title
+   xlab="Duration minutes")       # x-axis label

#### Exercise

Find the histogram of the eruption waiting period in faithful.