Question

I’m trying to test if all values in an object (if ordered) are adjacent integer values. For example:

x <- c(1,2,3)
is.adjacent(x)
TRUE

y <- c(1,2,4)
is.adjacent(y)
FALSE

z <- c(4,2,1,3)
is.adjacent(z)
TRUE

Any thoughts on a good approach?

Answer 1

Here’s a solution. I’ve constructed it so that it will return TRUE for a vector that contains a set of consecutive integers, even it some of them are repeated (e.g. c(1,3,2,1,1,1)). If you would like it to return FALSE in such cases, just remove the part that calls unique().

is.adjacent <- function(X) {
    all(diff(sort(unique(X))) == 1)
}

# Try it out
x <- c(1,2,3)
y <- c(1,2,4)
z <- c(4,2,1,3)

is.adjacent(x)
is.adjacent(y)
is.adjacent(z)