How to flag non-sequential numbers in R

user_7803155 0
Viewed 56

I was wondering if there's a way to flag non-consequential numbers? For instance below.

Number 
3         
4         
5         
6         
10        
11        
12        
16

Is there a way to flag the number before the non-sequential number like so?

Number  Flag
3         0
4         0
5         0
6         1
10        0
11        0
12        1
16     
etc..

Thank you!

r
3 Answers
dat$Flag <- +c(diff(dat$Number) != 1, NA)
dat
#   Number Flag
# 1      3    0
# 2      4    0
# 3      5    0
# 4      6    1
# 5     10    0
# 6     11    0
# 7     12    1
# 8     16   NA
user_33582720

I would use lead() here:

df$Flag <- as.numeric(lead(df$Number) != df$Number + 1)
df

  Number Flag
1      3    0
2      4    0
3      5    0
4      6    1
5     10    0
6     11    0
7     12    1
8     16   NA
user_18632290

Here's another option with data.table:

library(data.table)

setDT(df)[, Flag := +(shift(Number, type = "lead") - (Number + 1) != 0)]

Output

   Number  Flag
    <int> <int>
1:      3     0
2:      4     0
3:      5     0
4:      6     1
5:     10     0
6:     11     0
7:     12     1
8:     16    NA

Or another option with dplyr:

library(dplyr)

df %>%
  mutate(Flag = +(lead(Number) - (Number + 1) != 0))

Data

df <- structure(list(Number = c(3L, 4L, 5L, 6L, 10L, 11L, 12L, 16L)), class = "data.frame", row.names = c(NA, 
-8L))
user_152931910
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