我有一组数据mydata = data.frame(time,CODMn,NHN,RAIN)
其中time的数据和类型如下：
[1] "2018-04-01 00:00:00 UTC" "2018-04-01 04:00:00 UTC"
[3] "2018-04-01 08:00:00 UTC" "2018-04-01 12:00:00 UTC"
[5] "2018-04-01 16:00:00 UTC" "2018-04-01 20:00:00 UTC"
[7] "2018-04-02 00:00:00 UTC" "2018-04-02 04:00:00 UTC"
[9] "2018-04-02 08:00:00 UTC" "2018-04-02 12:00:00 UTC"
[11] "2018-04-02 16:00:00 UTC" "2018-04-02 20:00:00 UTC"
[13] "2018-04-03 00:00:00 UTC" "2018-04-03 04:00:00 UTC"
[15] "2018-04-03 08:00:00 UTC" "2018-04-03 12:00:00 UTC"
[17] "2018-04-03 16:00:00 UTC" "2018-04-03 20:00:00 UTC"
[19] "2018-04-04 00:00:00 UTC" "2018-04-04 04:00:00 UTC"
[21] "2018-04-04 08:00:00 UTC" "2018-04-04 12:00:00 UTC"
[23] "2018-04-04 16:00:00 UTC" "2018-04-04 20:00:00 UTC"
[25] "2018-04-05 00:00:00 UTC" "2018-04-05 04:00:00 UTC"
[27] "2018-04-05 08:00:00 UTC" "2018-04-05 12:00:00 UTC"
[29] "2018-04-05 16:00:00 UTC" "2018-04-05 20:00:00 UTC"
[31] "2018-04-06 00:00:00 UTC" "2018-04-06 04:00:00 UTC"
[33] "2018-04-06 08:00:00 UTC" "2018-04-06 12:00:00 UTC"
[35] "2018-04-06 16:00:00 UTC" "2018-04-06 20:00:00 UTC"
[37] "2018-04-07 00:00:00 UTC" "2018-04-07 04:00:00 UTC"
[39] "2018-04-07 08:00:00 UTC" "2018-04-07 12:00:00 UTC"
[41] "2018-04-07 16:00:00 UTC" "2018-04-07 20:00:00 UTC"


> class(time)
[1] "POSIXct" "POSIXt"



接着我使用ggplot绘制折线图，可以看到横坐标只有4.02，4.04，4.06，4.08这几天，但我想让每一个时间，包括日期和小时都显示出来，请问应该怎么做？