查找 NA 介于 0 和 1 之间的行

Question

我想识别包含 NA 且介于零和一之间的行。考虑这个data.table：

DT <- data.table(a = c(0, NA, NA, 0, NA, 1, 1, NA, 0, NA, 1, NA, NA, NA, 0, 1, 1, 0, NA, 0))

# DT
# a
# 1:  0
# 2: NA
# 3: NA
# 4:  0
# 5: NA
# 6:  1
# 7:  1
# 8: NA
# 9:  0
# 10: NA
# 11:  1
# 12: NA
# 13: NA
# 14: NA
# 15:  0
# 16:  1
# 17:  1
# 18:  0
# 19: NA
# 20:  0

如何识别行号。 5点、8点、10点和12点14分？

Answer 1

您可以尝试使用approx

DT[,b := approx((1:.N)[!is.na(a)],na.omit(a),1:.N)$y]

然后申请

DT[, which(is.na(a) & b>0 & b<1)]

或

DT[, which(is.na(a) & between(b, 0, 1, FALSE))]

给了

[1]  5  8 10 12 13 14

Answer 2

NA 序列的开头可以这样计算：

library("data.table")
DT <- data.table(a = c(0, NA, NA, 0, NA, 1, 1, NA, 0, NA, 1, NA, NA, NA, 0, 1, 1, 0, NA, 0))

r <- DT[, rle(is.na(a))]
R <- data.table(r$values, r$lengths, start=c(1, 1+head(cumsum(r$lengths), -1)))

i <- R[(V1), start]
j <- R[(V1), start+V2-1]
i[(DT[i-1, a] + DT[j+1, a])==1]
# result: [1]  5  8 10 12

Answer 3

zoo 包及其 na.locf() 函数可以帮助您，正如 Dirk Eddelbuettel 在此处所述：Replacing NAs with latest non-NA value。

library(data.table)
library(zoo)

DT <- data.table(a = c(0, NA, NA, 0, NA, 1, 1, NA, 0, NA, 1, NA, NA, NA, 0, 1, 1, 0, NA, 0))

non_nas <- DT[!is.na(a), a]
successor <- c(non_nas[-1], 0)
diff <- abs(non_nas - successor)
DT[!is.na(a), diff:=diff]

这将为您提供如下数据表：

     a diff
 1:  0    0
 2: NA   NA
 3: NA   NA
 4:  0    1
 5: NA   NA
 6:  1    0
 7:  1    1
 8: NA   NA
 9:  0    1
10: NA   NA
11:  1    1
12: NA   NA
13: NA   NA
14: NA   NA
15:  0    1
16:  1    0
17:  1    1
18:  0    0
19: NA   NA
20:  0    0

这里的想法是，diff 列中的每个“1”都告诉您，在下面的 NA 之后，“a”中的值会发生变化。

现在您想去掉“diff”列中的 NA。为清楚起见，我们将结果放入新列“b”中。这就是zoo 包发挥作用的地方：

DT[, b:=na.locf(diff)]

这会导致

     a diff b
 1:  0    0 0
 2: NA   NA 0
 3: NA   NA 0
 4:  0    1 1
 5: NA   NA 1
 6:  1    0 0
 7:  1    1 1
 8: NA   NA 1
 9:  0    1 1
10: NA   NA 1
11:  1    1 1
12: NA   NA 1
13: NA   NA 1
14: NA   NA 1
15:  0    1 1
16:  1    0 0
17:  1    1 1
18:  0    0 0
19: NA   NA 0
20:  0    0 0

最终

DT[is.na(a) & b == 1, which = TRUE]

会给你：

[1]  5  8 10 12 13 14