Well, here's one way.
# ...
for (Individual_Day in 1:2) {
Day_subset <- DF[DF$Day == as.integer(Individual_Day),]
lower <- with(Day_subset,as.POSIXct(strftime(min(time),"%Y-%m-%d")))
upper <- with(Day_subset,as.POSIXct(strftime(as.Date(max(time))+1,"%Y-%m-%d"))-1)
limits = c(lower,upper)
print(ggplot( data=Day_subset, aes( x=time, y=observation) ) +
geom_point() +
scale_x_datetime( breaks=("2 hour"),
minor_breaks=("1 hour"),
labels=date_format("%H:%M"),
limits=limits)
)
}
The calculation for lower
takes the minimum time in the subset and coerces it to character with only the date part (e.g., strips away the time part). Converting back to POSIXct generates the beginning of that day.
The calculation for upper
is a little more complicated. You have to convert the maximum time to a Date value and add 1 (e.g., 1 day), then convert to character (strip off the time part), convert back to POSIXct, and subtract 1 (e.g., 1 second). This generates 23:59 on the end day.
Huge amount of work for such a small thing. I hope someone else posts a simpler way to do this...