Question

I have the data frame df and I want to subset df based on a number sequence within a categorical.

 x  <- c(1,2,3,4,5,7,9,11,13)
 x2 <- x+77 
 df <- data.frame(x=c(x,x2),y= c(rep("A",9),rep("B",9)))

 df
    x y
1   1 A
2   2 A
3   3 A
4   4 A
5   5 A
6   7 A
7   9 A
8  11 A
9  13 A
10 78 B
11 79 B
12 80 B
13 81 B
14 82 B
15 84 B
16 86 B
17 88 B
18 90 B

I want only the rows where x increments by 1 and not the rows where x increases by two: e.g.

    x y
1   1 A
2   2 A
3   3 A
4   4 A
5   5 A
10 78 B
11 79 B
12 80 B
13 81 B
14 82 B

I figured I have to do some dort of subtraction between elements and check if the difference is >1 and combine this with a ddply but this seems cumbersome. Is there a sort of sequence function I am missing?

Answer 1

using diff

df[which(c(1,diff(df$x))==1),]