如何在R中使用ggplot2将日期和小时放在单独的字段中（并且是因子）

Question

相关这篇文章： How to plot when Date and hour in separate field using ggplot in R

我有数据框：

head(d[, c(1,2,7)], 10)
         date hour total_sess
2  2014-04-07   00        115
3  2014-04-07   01          3
4  2014-04-07   16          3
5  2014-04-07   21        115
6  2014-04-08   00        115
7  2014-04-08   06          3
8  2014-04-09   05          3
9  2014-04-09   11        201
10 2014-04-09   14          3
11 2014-04-09   20          3

>  str(d) 'data.frame': 55348 obs. of  9 variables:  $ date       :
> Factor w/ 3 levels "2014/04/07","2014/04/08",..: 1 1 1 1 1 1 1 1 1 1
> ...  $ hour       : Factor w/ 25 levels "00","01","02",..: 1 1 1 1 1 1
> 1 1 1 1 ...  $ total_sess : Factor w/ 711 levels "1","10","100",..:
> 594 413 209 1 1 327 1 1 1 48 ...

我想要做的是使用ggplot2绘制一个条形图，其中X轴=小时（沿轴指示日期），Y轴为total_sess，按照解决方案的帖子：

 "I would convert columns 'date' and 'hour' to as.POSIXct to use as x axis. In the data you show, 'hour' seems to be a character variable (leading zeroes), and you can create a time variable like this:

d$time <- as.POSIXct(paste0(d$date, " ", d$hour, ":00:00"))

'time'变量可以用作x变量，并且不一定需要按日期颜色（当然可以根据需要添加）。

ggplot(data = d, aes(x = time, y = total_sess)) +
  geom_bar(stat='identity') +
  theme_bw()" by @Henrik

我不确定如何组合日期和小时字段，并在类别因素时将它们转换为Posixct或posixlt？