gvisAnnotationChart(data, datevar = "", numvar = "", idvar = "",
titlevar = "", annotationvar = "", date.format = "%Y/%m/%d",
options = list(), chartid)data.frame. The data has to have at least two columns,
one with date information (datevar) and one numerical variable.data which shows the date dimension.
The information has to be of class Date or POSIX* time
series.data which shows the values to be
displayed against datevar. The information has to be
numeric.datevar is of class Date then
this argument specifies how the dates are reformatted to be used by
JavaScript.