[R] Shaded area

[George Brida]

Dear R users,

I have an xlsx file (attached to this mail) that shows the values of a
"der" series observed on a daily basis from January 1, 2017 to January 25,
2017. This series is strictly positive during two periods: from January 8,
2017 to January 11, 2017 and from January 16, 2017 to January 20, 2017. I
would like to plot the series with two shaded areas corresponding to the
positivity of the series. Specifically, I would like to draw 4 vertical
lines intersecting the x-axis in the 4 dates mentioned above and shade the
two areas of positivity. Thanks for your help.