r - 计算不同行的列之间的时间差(difftime)

Question

我有不同工作的“开始”和“结束”时间的数据，按“所有者”分组:

Data <- data.frame(
  job = c(1, 2, 3, 4, 5),
  owner = c("name1", "name2", "name1", "name1", "name2"),
  Start = as.POSIXct(c("2015-01-01 15:00:00", "2015-01-01 15:01:00", "2015-01-01 15:13:00", "2015-01-01 15:20:00", "2015-01-01 15:39:02"), format="%Y-%m-%d %H:%M:%S"),
  End =   as.POSIXct(c("2015-01-01 15:11:11", "2015-01-01 15:17:21", "2015-01-01 15:17:00", "2015-01-01 15:31:21", "2015-01-01 15:40:11"), format="%Y-%m-%d %H:%M:%S")
)

对于每个所有者，我想计算每个所有者的作业之间的空闲时间，即一个作业的“结束”时间与下一个作业的“开始”时间之间的差异。

如何使用 difftime() 计算特定行和不同列中时间之间的时间差？

结果应该是这样的:

job, owner, idletime
1, name1, NA
2, name2, NA
3, name1, 1.816667  # End of row 1 minus Start of row 3
4, name1, 3.0       # End of row 3 minus Start of row 4
...

Answer 1

这是一个可能的解决方案，使用 data.table

library(data.table) # v 1.9.5+
setDT(Data)[, idletime := difftime(Start, shift(End), units = "mins"), by = owner]
#    job owner               Start                 End       idletime
# 1:   1 name1 2015-01-01 15:00:00 2015-01-01 15:11:11        NA mins
# 2:   2 name2 2015-01-01 15:01:00 2015-01-01 15:17:21        NA mins
# 3:   3 name1 2015-01-01 15:13:00 2015-01-01 15:17:00  1.816667 mins
# 4:   4 name1 2015-01-01 15:20:00 2015-01-01 15:31:21  3.000000 mins
# 5:   5 name2 2015-01-01 15:39:02 2015-01-01 15:40:11 21.683333 mins

或者使用dplyr

library(dplyr)
Data %>%
  group_by(owner) %>%
  mutate(idletime = difftime(Start, lag(End), units = "mins"))

# Source: local data frame [5 x 5]
# Groups: owner
# 
#   job owner               Start                 End       idletime
# 1   1 name1 2015-01-01 15:00:00 2015-01-01 15:11:11        NA mins
# 2   2 name2 2015-01-01 15:01:00 2015-01-01 15:17:21        NA mins
# 3   3 name1 2015-01-01 15:13:00 2015-01-01 15:17:00  1.816667 mins
# 4   4 name1 2015-01-01 15:20:00 2015-01-01 15:31:21  3.000000 mins
# 5   5 name2 2015-01-01 15:39:02 2015-01-01 15:40:11 21.683333 mins