- A+

I have a vector of integers and I want to filter it by eliminating the components that are "isolated". What do I mean by "isolated"? those components that does not lie in an 4-neighbourhood of other component. The components in the vector are ordered increasingly, and there are no repetitions.

For example if I have `c(1,2,3,8,15,16,17)`

then I need to eliminate `8`

because is not in a 4-neighbourhood of other element.

I've tried applying

`for (p in 1:(length(index)-2)) if((index`

>3+index

)&(index

>3+index

)){index

`<-0} index<-index[index!=0]`

where `index`

is my vector of interest, but there's some problem with the logical condition. Could you please give me some hints?

Thanks in advance.

You can achieve it with a combination of `outer`

and `colSums`

, i.e.

`x[colSums(abs(outer(x, x, `-`)) >= 4) == length(x)-1] #[1] 8 `

To eliminate the values, we can do,

`i1 <- colSums(outer(x, x, FUN = function(i, j) abs(i - j) >= 4)) == length(x) - 1 x[!i1] #[1] 1 2 3 15 16 17 `

where,

`x <- c(1,2,3,8,15,16,17) `