I usually use ggplot2
to plot multiple data series, but if I don’t use ggplot2, there are **TWO**
simple ways to plot multiple data series in R. I’ll go over both today.

Matlab users can easily plot multiple data series in the same figure. They use **hold on**
and plot the data series as usual. Every data series goes into the same plot until they use **hold
off**.

But can the same thing be done in R? R is getting big as a programming language so plotting multiple data series in R should be trivial.

### The R points and lines way

**Solution 1**: just **plot** one data series and then use the **points**
or **lines** commands to plot the other data series in the same figure, creating the
multiple data series plot:

> plot(time, series1, type='l', xlab='t /s', ylab='s1') > points(time, series2, type='l') |

### Plot Multiple Data Series the Matlab way

**Solution 2**: this one mimics Matlab **hold on/off** behaviour. It uses the **new**
parameter of graphical devices. Let’s see how:

Setting **new** to **TRUE** tells R **NOT to clean** the previous frame before
drawing the new one. It’s a bit counter intuitive but R
is saying “*Hey, theres a new plot for the same figure so don’t erase whatever is
there before plotting the new data series*“.

Example (plot series2 on the same plot as series1):

> plot(time, series1, type='l', xlim=c(0.0,20.0), + ylim=c(0.0,1.0), xlab='t /s', ylab='s1') > par(new=T) > plot(time, series2, type='l', xlim=c(0.0,20.0), + ylim=c(0.0,1.0), xlab='', ylab='', axes=F) > par(new=F) |

The **par(new=T)** tells R to make the second plot without cleaning the first. Two things
to consider though: in the second set **axes** to FALSE, and **xlabel** and
**ylabel** to empty strings or in the final result you’ll see some overlapping and
bleeding of the several labels and axes.

Finally, because of all this superimposing you need to know your axes ranges and set them up equally in
all plot commands (**xlim**, and **ylim** in this example are set to the range
[0,20] and [0,1]).

R doesn’t automatically adjust the axes, as it doesn’t use the first frame as reference or
the multiple data series. You need to supply these values or you’ll end up with a wrong looking
plot ~~like Marge Simpson’s hair~~.

In conclusion, either solution will work to plot multiple data series inside R, but sometimes one will be better than the other. Sometimes your data series represent different properties and you’ll need to specify the y ranges individually. In this case the latter option might be useful. Other times you just want a quick exploratory data analysis plot, or your data series are measuring the same property and the former method suffices.