R 使用 data.table 来削减包含 2 个或更多变量的固定时间间隔

Question

我有一个数据框

df <- data.frame(time = c("2015-09-07 00:32:19", "2015-09-07 01:02:30", "2015-09-07 01:31:36", "2015-09-07 01:47:45",
"2015-09-07 02:00:17", "2015-09-07 02:07:30", "2015-09-07 03:39:41", "2015-09-07 04:04:21", "2015-09-07 04:04:21", "2015-09-07 04:04:22"), 
inOut = c("IN", "OUT", "IN", "IN", "IN", "IN", "IN", "OUT", "IN", "OUT")) 

> df
                  time inOut
1  2015-09-07 00:32:19    IN
2  2015-09-07 01:02:30   OUT
3  2015-09-07 01:31:36    IN
4  2015-09-07 01:47:45    IN
5  2015-09-07 02:00:17    IN
6  2015-09-07 02:07:30    IN
7  2015-09-07 03:39:41    IN
8  2015-09-07 04:04:21   OUT
9  2015-09-07 04:04:21    IN
10 2015-09-07 04:04:22   OUT
>

我想计算每 15 分钟 IN/OUT 的计数，我可以通过创建另一个 in_df、out_df 来做到这一点，每 15 分钟切割一次这些数据帧，然后将它们合并在一起以获得我的结果。 outdf 是我的预期结果。

in_df <- df[which(df$inOut== "IN"),]
out_df <- df[which(df$inOut== "OUT"),]

a <- data.frame(table(cut(as.POSIXct(in_df$time), breaks="15 mins")))
b <- data.frame(table(cut(as.POSIXct(out_df$time), breaks="15 mins")))
colnames(b) <- c("Time", "Out")
colnames(a) <- c("Time", "In")

outdf <- merge(a,b, all=TRUE)
outdf[is.na(outdf)] <- 0

> outdf
                  Time In Out
1  2015-09-07 00:32:00  1   0
2  2015-09-07 00:47:00  0   0
3  2015-09-07 01:02:00  0   1
4  2015-09-07 01:17:00  1   0
5  2015-09-07 01:32:00  0   0
6  2015-09-07 01:47:00  2   0
7  2015-09-07 02:02:00  1   0
8  2015-09-07 02:17:00  0   0
9  2015-09-07 02:32:00  0   0
10 2015-09-07 02:47:00  0   0
11 2015-09-07 03:02:00  0   0
12 2015-09-07 03:17:00  0   0
13 2015-09-07 03:32:00  1   0
14 2015-09-07 03:47:00  0   0
15 2015-09-07 04:02:00  1   2

我的问题是如何使用 data.table 来获得相同的结果？

Answer 1

在data.table，我会

library(data.table)
setDT(df)

df[, timeCut := cut(as.POSIXct(time), breaks="15 mins")]

df[J(timeCut = levels(timeCut)), 
   as.list(table(inOut)), 
   on = "timeCut", 
   by = .EACHI]

给出：

                timeCut IN OUT
 1: 2015-09-07 00:32:00  1   0
 2: 2015-09-07 00:47:00  0   0
 3: 2015-09-07 01:02:00  0   1
 4: 2015-09-07 01:17:00  1   0
 5: 2015-09-07 01:32:00  0   0
 6: 2015-09-07 01:47:00  2   0
 7: 2015-09-07 02:02:00  1   0
 8: 2015-09-07 02:17:00  0   0
 9: 2015-09-07 02:32:00  0   0
10: 2015-09-07 02:47:00  0   0
11: 2015-09-07 03:02:00  0   0
12: 2015-09-07 03:17:00  0   0
13: 2015-09-07 03:32:00  1   0
14: 2015-09-07 03:47:00  0   0
15: 2015-09-07 04:02:00  1   2

解释最后一部分像DT[i=J(x=my_x), j, on="x", by=.EACHI]，可以读作：

在 my_x 上加入 DT 列 x。
然后对 my_x 确定的每个子集执行 j。

在这种情况下，j=as.list(table(inOut))。必须将 table 强制转换为列表以创建多个列（inOut 的每个级别一个）。

R 使用 data.table 来削减包含 2 个或更多变量的固定时间间隔

R using data.table to cut fix time interval that contain 2 or more variables

r

data.table