data.table基于组的滞后值删除行

Question

我有一个data.table以下形式:

DT <- data.table(tag = rep(c("A", "B"), each = 10),
                 value =  c(0, 3, 3, 3, 0, 1, 1, 1, 3, 0,
                            0, 1, 3, 1, 0, 3, 0, 1, 1, 0))
> DT
    tag value
 1:   A     0
 2:   A     3
 3:   A     3
 4:   A     3
 5:   A     0
 6:   A     1
 7:   A     1
 8:   A     1
 9:   A     3
10:   A     0
11:   B     0
12:   B     1
13:   B     3
14:   B     1
15:   B     0
16:   B     3
17:   B     0
18:   B     1
19:   B     1
20:   B     0

我想删除所有值为3但仍然只有0的行.这是我想删除第2,3,4和16行,但需要保留第9行和第13行.

有办法执行此操作吗？

Answer 1

可能的解决方案:

DT[, `:=` (threes = rleid(value==3), apz = value == 3 & shift(value) == 0)
   ][, if (all(!apz)) .SD, by = threes
     ][, c('threes','apz') := NULL]

这使:

    tag value
 1:   A     0
 2:   A     0
 3:   A     1
 4:   A     1
 5:   A     1
 6:   A     3
 7:   A     0
 8:   B     0
 9:   B     1
10:   B     3
11:   B     1
12:   B     0
13:   B     0
14:   B     1
15:   B     1
16:   B     0