有条件地计算R中行之间的时间差

我试图计算一行和一列满足某些条件的行之间的时间差

读取一些数据：

my_data <- data.frame(criteria = c("some text", "some more text", " ", " ", "more text", " "),
                  timestamp = as.POSIXct(c("2015-07-30 15:53:15", "2015-07-30 15:53:47", "2015-07-30 15:54:48", "2015-07-30 15:55:48", "2015-07-30 15:56:48", "2015-07-30 15:57:49")))

        criteria           timestamp
1      some text 2015-07-30 15:53:15
2 some more text 2015-07-30 15:53:47
3                2015-07-30 15:54:48
4                2015-07-30 15:55:48
5      more text 2015-07-30 15:56:48
6                2015-07-30 15:57:49

到目前为止，我已经构建了代码来识别“0”应该在哪里——我只需要代码来填充时间差。这是我的密码：

my_data$time_diff <- ifelse (my_data$criteria != "", # Here's our statement
  my_data$time_diff <- "0", # Here's what happens if statement is TRUE
  my_data$time_diff <- NEED CODE HERE # if statement FALSE
  )

---

my_data$time_diff用alexis_laz熟练的表达完成答案：

my_data <- data.frame(criteria = c("some text", "some more text", " ", " ", "more text", " "),
                      timestamp = as.POSIXct(c("2015-07-30 15:53:15", "2015-07-30 15:53:47", "2015-07-30 15:54:48", "2015-07-30 15:55:48", "2015-07-30 15:56:48", "2015-07-30 15:57:49")))

my_data$time_diff <- 
  my_data$timestamp - 
  my_data[cummax((my_data$criteria != " ") * seq_len(nrow(my_data))), 'timestamp']

my_data

        criteria           timestamp time_diff
1      some text 2015-07-30 15:53:15    0 secs
2 some more text 2015-07-30 15:53:47    0 secs
3                2015-07-30 15:54:48   61 secs
4                2015-07-30 15:55:48  121 secs
5      more text 2015-07-30 15:56:48    0 secs
6                2015-07-30 15:57:49   61 secs

my_data似乎每个“时间戳”都需要与cummax处的“时间戳”的时间差（（my_data$criteria！=“”）*seq_len（nrow（my_data））
repsectively？@alexis_laz，我想是这样的。为了澄清您的意思，我将每个时间戳（例如“timestamp3”）与“timestamp3”上方最大行号的时间戳进行比较，其中
my_data$criteria！=“”
。那读数正确吗？如果是这样，那么是的。作为一个额外的注意事项，
difftime
在这里也很方便，它的
units=“mins”
参数
my_data <- data.frame(criteria = c("some text", "some more text", " ", " ", "more text", " "),
                      timestamp = as.POSIXct(c("2015-07-30 15:53:15", "2015-07-30 15:53:47", "2015-07-30 15:54:48", "2015-07-30 15:55:48", "2015-07-30 15:56:48", "2015-07-30 15:57:49")))

my_data$time_diff <- 
  my_data$timestamp - 
  my_data[cummax((my_data$criteria != " ") * seq_len(nrow(my_data))), 'timestamp']

my_data

        criteria           timestamp time_diff
1      some text 2015-07-30 15:53:15    0 secs
2 some more text 2015-07-30 15:53:47    0 secs
3                2015-07-30 15:54:48   61 secs
4                2015-07-30 15:55:48  121 secs
5      more text 2015-07-30 15:56:48    0 secs
6                2015-07-30 15:57:49   61 secs