Line Charts

A line chart or line graph is a type of chart that displays information as a series of data points called markers connected by straight line segments.

ggplot uses an elegant geom() method, which helps in quickly switching between two visual objects. In the previous example, we saw geom_point() for the scatterplot. In line charts, the observations are connected by a line in the order of the variable on the x-axis. The shaded area surrounding the line represents the 95% confidence interval, that is, there is 95% confidence that the actual regression line lies within the shaded area. We will discuss more on this idea in Chapter 4, Regression.

In the following plot, we show the line chart of age and bank balance for single, married, and divorced individuals. It is not clear whether there is some trend, but one can see the pattern among the three categories:

ggplot(data = df_bank_detail) +
  geom_smooth(mapping = aes(x = age, y = balance, linetype = marital))
## 'geom_smooth()' using method = 'gam'

Figure 1.10: Line graph of age and balance