R 的时间差

我有一些数据，如下所示：

id    time
1     2013-02-04 02:20:59
1     2013-02-04 02:21:05
1     2013-02-04 02:21:24
2     2013-02-04 02:21:26
2     2013-02-04 02:22:19
2     2013-02-04 02:22:35

我想获取两个时间值之间每个 id 的时间差，例如：

id 1 02:21:05-02:20:59=00:00:06. 

我怎样才能在 R 中做到这一点？

你应该做diff准时以及id然后使用ifelse填充第三列

df <- structure(list(id = c(1L, 1L, 1L, 2L, 2L, 2L), 
        time = structure(c(1359915659, 1359915665, 1359915684, 
        1359915686, 1359915739, 1359915755), class = c("POSIXct", 
        "POSIXt"), tzone = "")), .Names = c("id", "time"), row.names = c(NA, -6L), 
        class = "data.frame")
df
##   id                time
## 1  1 2013-02-04 02:20:59
## 2  1 2013-02-04 02:21:05
## 3  1 2013-02-04 02:21:24
## 4  2 2013-02-04 02:21:26
## 5  2 2013-02-04 02:22:19
## 6  2 2013-02-04 02:22:35

## here you are checking if that result is diff in time only when diff in id is 0
df$result <- c(0, ifelse(diff(df$id) == 0, diff(df$time), 0))

df
##   id                time result
## 1  1 2013-02-04 02:20:59      0
## 2  1 2013-02-04 02:21:05      6
## 3  1 2013-02-04 02:21:24     19
## 4  2 2013-02-04 02:21:26      0
## 5  2 2013-02-04 02:22:19     53
## 6  2 2013-02-04 02:22:35     16