Cumulating neighbours lists

You can cumulate multiple neighbour lists to a single neighbour list:
nblag_cumul(<list of neighbours lists>)

Cumulating the 1st and 2nd order neighbours lists from before:

nblagsc <- nblag_cumul(nblags[1:2])
class(nblagsc)

## [1] "nb"

head(nblagsc)

## [[1]]
## [1] 2 3 4 5
## 
## [[2]]
## [1] 1 3 4 5 8
## 
## [[3]]
##  [1]  1  2  4  5  6  8  9 11 15 16
## 
## [[4]]
##  [1]  1  2  3  5  6  7  8  9 11 12 13 15 16
## 
## [[5]]
##  [1]  1  2  3  4  6  7  8  9 10 11 12 13 14 15 16 18 20 22 24 25 26
## 
## [[6]]
##  [1]  3  4  5  8  9 10 11 15 16 20 22 25 26