用ggplot2绘制x轴上的日期和y轴上的时间

I have read in a series of 37 dates and times that an event happened. It is now sitting as a POSIXlt object. I want a graphic representation of the times that the events happened on each day. So the x axis should be the date and y axis should be the time of day.I have read in a series of 37 dates and times t