[R] ggplot2: formula for bar width in geom_bar?

[J Toll]

Hi,

I'm trying to figure out the formula used by ggplot2 to calculate the
width of a bar in geom_bar so that I can use that elsewhere in the
plot.  My code looks like this:

 ggplot(xAll, aes(Date)) +
   geom_bar(subset = .(Direction == "Up"), aes(y = Change, fill =
Time), stat = "identity") +
   geom_bar(subset = .(Direction == "Down"), aes(y = Change, fill =
Time), stat = "identity") +
   geom_segment(data = xline,
                aes(Date, Total,
                    xend = Date,
                    yend = (Total - (sign(Total) * (mean(Total)/25)))),
                size = 5,     # this is where I need to substitute in
the geom_bar width
                color = "white")

Right now, I have to manually adjust (i.e. guess) the size of
geom_segment so that it matches the width of geom_bar.  Can someone
point me to the formula used by geom_bar to calculate bar width?  I've
attached an example plot for reference.

Thanks,


James
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