r - data.table: “group counter” 对于特定的列组合

Question

我想根据一组相同的行在数据框中添加一个计数器列。为此，我使用了包 data.table。在我的例子中，行之间的比较需要从列“z”和(“x”或“y”)的组合中进行。

我测试了:

DF[ , Index := .GRP, by = c("x","y","z") ]

但结果是“z”AND“x”AND“y”的组合。

我怎样才能得到 "z"AND ("x"OR "y") 的组合？

这是一个数据示例:

DF = data.frame(x=c("a","a","a","b","c","d","e","f","f"), y=c(1,3,2,8,8,4,4,6,0), z=c("M","M","M","F","F","M","M","F","F"))
DF <- data.table(DF)

我想要这样的输出:

> DF
   x y z Index
1: a 1 M   1
2: a 3 M   1
3: a 2 M   1
4: b 8 F   2
5: c 8 F   2
6: d 4 M   3
7: e 4 M   3
8: f 6 F   4
9: f 0 F   4

Answer 1

如果 z 的值或 x 和 的值发生变化，则新组开始 y 正在改变。

试试这个例子。

require(data.table)

DF <- data.table(x = c("a","a","a","b","c","d","e","f","f"),
                 y = c(1,3,2,8,8,4,4,6,0),
                 z=c("M","M","M","F","F","M","M","F","F"))

# The functions to compare if value is not equal with the previous value
is.not.eq.with.lag <- function(x) c(T, tail(x, -1) != head(x, -1))

DF[, x1 := is.not.eq.with.lag(x)]
DF[, y1 := is.not.eq.with.lag(y)]
DF[, z1 := is.not.eq.with.lag(z)]
DF

DF[, Index := cumsum(z1 | (x1 & y1))]
DF