[R] Generate and store multiple plots

[analyst41 at hotmail.com]

I have a data set whose rows look like

Item date variable_1 variable_2 variable_3 variable_4


Different items may occur over different dates.

During any single study, I might select a subset of the four variables
or some function of them to be plotted against time (date).

For each item, I would select a date range and I want a plot of the
selected variables over that range for that item.

I need a method that would do this at one shot and put the plot
objects out to disk, one for each item.

Thanks.