R 数据表 - 使用当前行之前的所有行计算每一行

Question

我希望按 id 和按顺序(时间)计算不同的东西。
例如，与:

dt = data.table( id=c(1,1,1,2,2,2,3,3,3), hour=c(1,5,5,6,7,8,23,23,23), ip=c(1,1,45,2,2,2,3,1,1), target=c(1,0,0,1,1,1,1,1,0), day=c(1,1,1,1,1,1,3,2,1))

   id hour ip target day
1:  1    1  1      1   1
2:  1    5  1      0   1
3:  1    5 45      0   1
4:  2    6  2      1   1
5:  2    7  2      1   1
6:  2    8  2      1   1
7:  3   23  3      1   3
8:  3   23  1      1   2
9:  3   23  1      0   1

我希望为每个 id 计算到目前为止每行的事件天数和事件小时数。
这意味着我希望获得以下输出:

   id hour ip target day  nb_active_hours_so_far
1:  1    1  1      1   1  0  (first occurence of id when ordered by hour)
2:  1    5  1      0   1  1  (has been active in hour "1")
3:  1    5 45      0   1  2  (has been active in hour "1" and "5")
4:  2    6  2      1   1  0  (first occurence)
5:  2    7  2      1   1  1  (has been active in hour "6")
6:  2    8  2      1   1  2  (has been active in hour "6" and "7")
7:  3   23  3      1   3  0  (first occurence)
8:  3   23  1      1   2  1  (has been active in hour "23")
9:  3   23  1      0   1  1  (has been active in hour "23" only)

要获得事件时间的总数，我会这样做:

dt[, nb_active_hours := length(unique(hour)), by=id]

但我也想拥有到目前为止的部分。我不知道如何去做...
任何帮助，将不胜感激。

Answer 1

这似乎有效(尽管尚未在不同情况下进行测试)

dt[, nb_active_hours_so_far := cumsum(c(0:1, diff(hour[-.N]))>0), by = id]
#    id hour ip target day temp nb_active_hours_so_far
# 1:  1    1  1      1   1    0                      0
# 2:  1    5  1      0   1    1                      1
# 3:  1    5 45      0   1    1                      2
# 4:  2    6  2      1   1    0                      0
# 5:  2    7  2      1   1    1                      1
# 6:  2    8  2      1   1    2                      2
# 7:  3   23  3      1   3    0                      0
# 8:  3   23  1      1   2    0                      1
# 9:  3   23  1      0   1    0                      1