Error plotting dates after session refresh

[mjhendrickson]

ggplot(data = HxMx) + geom_bar(mapping = aes(x = start_time_DI)) + scale_x_date(name = " ") + scale_y_continuous(name = " ", labels = comma) + theme(axis.title.x = element_blank(), axis.text.x = element_text(angle = 90, vjust = 0.5)) + labs(title = "Start Time")

Results in
Error: Invalid input: date_trans works with objects of class Date only

[mjhendrickson]

After fix in #7, a new error results when running the above code.
Error in check_breaks_labels(breaks, labels) : object 'comma' not found

[mjhendrickson]

Removing labels = comma from the scale_y_continous argument alleviates the issue.