在数据框中查找连续值

Question

I have a dataframe. I wish to detect consecutive numbers and populate a new column as 1 or 0.

  ID Val
1  a   8
2  a   7
3  a   5
4  a   4
5  a   3
6  a   1

Expected output

  ID Val  outP
1  a   8  0
2  a   7  1
3  a   5  0
4  a   4  1
5  a   3  1
6  a   1  0

Answer 1

You could do this with the diff function in combination with abs and see whether the outcome is 1 or another value:

d$outP <- c(0, abs(diff(d$Val)) == 1)

which gives:

> d
  ID Val outP
1  a   8    0
2  a   7    1
3  a   5    0
4  a   4    1
5  a   3    1
6  a   1    0

If you only want to take decreasing consecutive values into account, you can use:

c(0, diff(d$Val) == -1)

When you want to do this for each ID , you can also do this in base R or with dplyr :

# base R
d$outP <- ave(d$Val, d$ID, FUN = function(x) c(0, abs(diff(x)) == 1))

# dplyr
library(dplyr)
d %>% 
  group_by(ID) %>% 
  mutate(outP = c(0, abs(diff(Val)) == 1))

Answer 2

We can also a faster option by comparing the previous value with current

 with(df1, as.integer(c(FALSE, Val[-length(Val)] - Val[-1]) ==1))
 #[1] 0 1 0 1 1 0

---

If we need to group by "ID", one option is data.table

 library(data.table)
 setDT(df1)[,  outP := as.integer((shift(Val, fill =Val[1]) - Val)==1) , by = ID]