R:如何从日期时间添加卷

Question

我有以下数据:

 df <-
Session    Volume                    StartTime                 EndTime
1         27,75          2016-01-22 17:00:33.707  2016-01-27 06:02:54.900
2         10,78          2016-01-22 14:31:22.127  2016-01-23 15:01:20.997
3         15,88          2016-01-27 12:46:18.660  2016-01-27 15:01:23.250
4         46,10          2016-01-25 16:01:34.613  2016-01-25 21:46:35.477
5         94,60          2016-01-27 05:38:06.597  2016-01-27 06:08:06.027
6         15,93          2016-01-20 16:15:59.350  2016-01-21 06:06:43.933

我想添加每天(在开始时间)的数据以接收包含每天所有 session 总音量的数据集，以便我可以随时间绘制音量。例如。 2016 年 1 月 22 日，总共收费 38.53。
以便

dfnew <- 
 Day            TotalVolume
2016-01-22    38.53
2016-01-25    46.10
2016-01-27    110.48
 etc. 

执行此操作的最有效方法是什么？

Answer 1

带数据表

library(data.table)
df[,StartTime := as.POSIXct(StartTime)]
df[,sum(Volume), by = as.Date(df$StartTime)]


      as.Date     V1
1: 2016-01-22  38.53
2: 2016-01-27 110.48
3: 2016-01-25  46.10
4: 2016-01-20  15.93

和 dplyr

library(dplyr)
df %>%
  mutate(StartTime = as.POSIXct(StartTime)) %>%
  group_by(as.Date(StartTime)) %>%
  summarise(sum(Volume))

以下是数据:

df <- as.data.table(read.table(text = "
  Session;    Volume;                    StartTime;                 EndTime
1;         27,75;          2016-01-22 17:00:33.707;  2016-01-27 06:02:54.900
2;         10,78;          2016-01-22 14:31:22.127;  2016-01-23 15:01:20.997
3;         15,88;          2016-01-27 12:46:18.660;  2016-01-27 15:01:23.250
4;         46,10;          2016-01-25 16:01:34.613;  2016-01-25 21:46:35.477
5;         94,60;          2016-01-27 05:38:06.597;  2016-01-27 06:08:06.027
6;         15,93;          2016-01-20 16:15:59.350;  2016-01-21 06:06:43.933",header = T,sep = ";",dec = ","))