Adding an extra series to an existing chart
A great way to visually compare two times series is to display them on the same chart with different scales.
Suppose you already have a plot of mydata
. As you saw in the video, you can use lines(mydata2)
to add a new time series mydata2
to this existing plot. If you want a scale for this time series on the right side of the plot with equally spaced tick marks, use axis(side, at)
, where side
is an integer specifying which side of the plot the axis should be drawn on, and at
is set equal to pretty(mydata2)
.
Finally, to distinguish these two time series, you can add a legend with the legend()
function. Let's examine the one used in the video:
> # x specifies location of legend in plot
> legend(x = "bottomright",
# legend specifies text label(s)
legend = c("Stock X", "Stock Y"),
# col specifies color(s)
col = c("black", "red"),
# lty specifies line type(s)
lty = c(1, 1))
Since there are two time series in the plot, some options in legend()
are set to a vector of length two.
In this exercise, you will create a plot and legend for two time series. The same dataset data
is provided for you.
This exercise is part of the course
Visualizing Time Series Data in R
Exercise instructions
- Plot the "microsoft" series and add the title "Stock prices since 2015"
- Add the "dow_chemical" series to the chart as a red line using
lines()
- Add an appropriately scaled Y axis on the right side of the chart for the "dow_chemical" data using
axis()
andpretty()
- Add an appropriately colored legend in the bottom right corner labeled with the names of the stocks and regular lines
Hands-on interactive exercise
Have a go at this exercise by completing this sample code.
# Plot the "microsoft" series
# Add the "dow_chemical" series in red
# Add a Y axis on the right side of the chart
# Add a legend in the bottom right corner