pl.2tsgg: Time series plot for two variables with ggplot2
Description
Plotting two time series in one plot, with title and label. If both variables are time series object, they will be merged by time.
If both variables are not time series object, they will be merged by order. The first variable is set to be a solid line and the second variable
is set to be a dashed line. If the variables are of different type a warning message will be given.