# Line Charts

## Overview

Line charts are created with the function **lines(***x* **,** *y***, type=)** where *x* and *y* are numeric vectors of (x,y) points to connect. **type=** can take the following values:

type |
description |

p |
points |

l |
lines |

o |
overplotted points and lines |

b, c |
points (empty if "c") joined by lines |

s, S |
stair steps |

h |
histogram-like vertical lines |

n |
does not produce any points or lines |

The **lines( )** function *adds* information to a graph. It can not produce a graph on its own. Usually it follows a **plot(***x* **,** *y***)** command that produces a graph.

By default, **plot( )** plots the (x,y) points. Use the **type="n"** option in the **plot( )** command, to create the graph with axes, titles, etc., but *without* plotting the points.

## Example

In the following code each of the **type=** options is applied to the same dataset. The **plot( )** command sets up the graph, but ** does not** plot the points.

```
x <- c(1:5); y <- x # create some data
par(pch=22, col="red") # plotting symbol and color
par(mfrow=c(2,4)) # all plots on one page
opts = c("p","l","o","b","c","s","S","h")
for(i in 1:length(opts)){
heading = paste("type=",opts[i])
plot(x, y, type="n", main=heading)
lines(x, y, type=opts[i])
}
```

Next, we demonstrate each of the **type=** options when **plot( )** sets up the graph and _ **does** _ plot the points.

```
x <- c(1:5); y <- x # create some data
par(pch=22, col="blue") # plotting symbol and color
par(mfrow=c(2,4)) # all plots on one page
opts = c("p","l","o","b","c","s","S","h")
for(i in 1:length(opts){
heading = paste("type=",opts[i])
plot(x, y, main=heading)
lines(x, y, type=opts[i])
}
```

As you can see, the **type="c"** option only looks different from the **type="b"** option if the plotting of points is suppressed in the **plot( )** command.

To demonstrate the creation of a more complex line chart, let's plot the growth of 5 orange trees over time. Each tree will have its own distinctive line. The data come from the dataset **Orange**.

```
# Create Line Chart
# convert factor to numeric for convenience
Orange$Tree <- as.numeric(Orange$Tree)
ntrees <- max(Orange$Tree)
# get the range for the x and y axis
xrange <- range(Orange$age)
yrange <- range(Orange$circumference)
# set up the plot
plot(xrange, yrange, type="n", xlab="Age (days)",
ylab="Circumference (mm)" )
colors <- rainbow(ntrees)
linetype <- c(1:ntrees)
plotchar <- seq(18,18+ntrees,1)
# add lines
for (i in 1:ntrees) {
tree <- subset(Orange, Tree==i)
lines(tree$age, tree$circumference, type="b", lwd=1.5,
lty=linetype[i], col=colors[i], pch=plotchar[i])
}
# add a title and subtitle
title("Tree Growth", "example of line plot")
# add a legend
legend(xrange[1], yrange[2], 1:ntrees, cex=0.8, col=colors,
pch=plotchar, lty=linetype, title="Tree")
```

## Going Further

Try the exercises in this course on plotting and data visualization in R.