Let's see how to produce multiple curves in ggplot. We use the Children dataset (refer to the Creating multiple curves simultaneously section in Chapter 3, Mastering the qplot Function) to produce a line graph of height against age for each child. We created this particular graph in qplot and now we create it in ggplot, but we amend it a little. You can cut and paste the data directly from the code file for this chapter. Remember that the data for each child is arranged in a single column that holds six measurements of height for each child. We will include large points (size = 3) and slightly heavier lines (lwd = 1.2) using geom_point() and geom_line(), respectively. We will also map a color to the variable Child, so that both points and lines have a unique color for each child.

Finally, we impose our own color scheme using scale_color_manual():

ggplot(cheight, aes(x=Age, y=Height, color = factor(Child))) + geom_point(size = 3) +  geom_line(lwd = 0.7) + labs(title = "Childrens' Growth Patterns") + labs(x = "Age (years)", y = "HEIGHT (cm)") + scale_color_manual(values = c("red", "yellow", "blue", "darkgreen"))

Now we get this graph:

The arrangement of the data within a single column made it easy to create a graph with all four curves at once.