根据列中的序列中断对数据帧进行分组? [英] Group a dataframe based on sequence breaks in a column?
问题描述
我有一个data.frame,它有一列整数值。我需要形成一个分组变量,以标识该列中的序列中断。例如,我可以创建另一列升序整数,每当原始列的值不大于其滞后值时就添加一个。我该怎么做?
I have a data.frame, which has a column of integer values. I need to form a grouping variable that identifies sequence breaks in that column. For instance, I could create another column of ascending integers that adds one whenever the original column's value is not greater than its lagged value. How do I do this?
例如如果我有这样的data.frame:
E.g. if I have a data.frame like this:
df <- data.frame(A = c(1,2,4,6,78,3,56,78,23))
我需要一些生产方法带有B列的新表:
I need some way to produce new table with column B:
df$B <- c(1,1,1,1,1,2,2,2,3)
我尝试过例如与 dplyr
:
df %>% mutate(B = 1,
B = case_when(A < lag(A), B + 1))
That is not quite correct.
推荐答案
我们可以使用 cumsum
和 diff
会在每次序列中断时增加值
We can use cumsum
and diff
which will increment the value every time the sequence is broken
cumsum(c(-1, diff(df$A)) < 0)
#[1] 1 1 1 1 1 2 2 2 3
我们还可以集成到 dplyr
链中以获得
library(dplyr)
df %>%
mutate(B = cumsum(c(-1, diff(A)) < 0))
# A B
#1 1 1
#2 2 1
#3 4 1
#4 6 1
#5 78 1
#6 3 2
#7 56 2
#8 78 2
#9 23 3
使用 lag
可能是
df %>%
mutate(B = cumsum(c(-1, (A - lag(A))[-1]) < 0))
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