减去 2 个不同行中的数据

Question

我有从数据库中每隔一段时间收集的数据。指标是计数器，不断增加。要获得给定时间的度量值，您必须从同一行的先前版本中减去一行。

例子：

                 TS INST_ID         EVENT WAIT_TIME_MILLI WAIT_COUNT
2014-01-29 17:20:36       1 log file sync               1     756873
2014-01-29 17:20:36       1 log file sync               2      15627
2014-01-29 17:20:36       1 log file sync               4       2925
2014-01-29 17:21:03       1 log file sync               1     761063
2014-01-29 17:21:03       1 log file sync               2      15659
2014-01-29 17:21:03       1 log file sync               4       2929

期望输出：

                 TS INST_ID         EVENT WAIT_TIME_MILLI WAIT_COUNT
2014-01-29 17:21:03       1 log file sync               1       4190
2014-01-29 17:21:03       1 log file sync               2         32
2014-01-29 17:21:03       1 log file sync               4          4

TS 是收集指标的时间。INST_ID、EVENT 和 WAIT_TIME_MILLI 是静态标识符。我想计算从一个 TS 到下一个 WAIT_COUNT 的增量。

我已经稍微简化了数据，但如果重要的话，有很多事件并且可以是多个 INST_ID。

这是测试数据框：

structure(list(TS = structure(c(1391034063.541, 1391034063.541, 
1391034063.541, 1391034036.136, 1391034036.136, 1391034036.136
), class = c("POSIXct", "POSIXt")), INST_ID = c(1, 1, 1, 1, 1, 
1), EVENT = c("log file sync", "log file sync", "log file sync", 
"log file sync", "log file sync", "log file sync"), WAIT_TIME_MILLI = c(1, 
2, 4, 1, 2, 4), WAIT_COUNT = c(761063, 15659, 2929, 756873, 15627, 
2925)), .Names = c("TS", "INST_ID", "EVENT", "WAIT_TIME_MILLI", 
"WAIT_COUNT"), class = "data.frame", row.names = c(NA, 6L))

Answer 1

如果您的数据是名为 dat 的 data.frame

library(dplyr)
dat <- arrange(dat, WAIT_TIME_MILLI, TS)
dat <- group_by(dat, WAIT_TIME_MILLI)
dat <- mutate(dat, diff = WAIT_COUNT - lag(WAIT_COUNT))
filter(dat, !is.na(diff))

或者：

library(dplyr)
dat %.%
  arrange(WAIT_TIME_MILLI, TS) %.%
  group_by(WAIT_TIME_MILLI) %.%
  mutate(diff = WAIT_COUNT - lag(WAIT_COUNT)) %.%
  filter(!is.na(diff))