我正在尝试使用 dplyr 包计算两个相邻行中两个时间戳之间的时间差。这是代码:
tidy_ex <- function () {
library(dplyr)
#construct example data
data <- data.frame(code = c(10888, 10888, 10888, 10888, 10888, 10888,
10889, 10889, 10889, 10889, 10889, 10889,
10890, 10890, 10890),
station = c("F1", "F3", "F4", "F5", "L5", "L7", "F1",
"F3", "F4", "L5", "L6", "L7", "F1", "F3", "F5"),
timestamp = c(1365895151, 1365969188, 1366105495,
1367433149, 1368005216, 1368011698,
1366244224, 1366414926, 1367513240,
1367790556, 1367946420, 1367923973,
1365896546, 1365907968, 1366144207))
# reformat timestamp as POSIXct
data$timestamp <- as.POSIXct(data$timestamp,origin = "1970-01-01")
#create tbl_df
data2 <- tbl_df(data)
#group by code and calculate time differences between two rows in timestamp column
data2 <- data2 %>%
group_by(code) %>%
mutate(diff = c(difftime(tail(timestamp, -1), head(timestamp, -1))))
data2
}
该代码产生一条错误消息:
Error: incompatible size (5), expecting 6 (the group size) or 1
我猜这是因为最后一行的差异产生了 NA(因为没有进一步的相邻行)。然而 difftime/head-tails 方法适用于 plyr 包而不是 dplyr(请参阅此 StackOverflow 帖子) https://stackoverflow.com/questions/17015425/difftime-between-2-columns-and-next-row-within-a-variable
我怎样才能使用 dplyr 让它工作?