Given an object of class "spatial.neighbor" detects spatial units that
have no neighbors (islands).
USAGE:
check.islands(x, remap=F)
REQUIRED ARGUMENTS:
x:
an object of class "spatial.neighbor".
OPTIONAL ARGUMENTS:
remap:
logical flag: if there is an island, should we recode the indexing of
the spatial contiguity matrix to eliminate the rows and columns with all
zeroes? That is, should we renumber components row.id and col.id of
the spatial neighbor object?
VALUE:
if remap=FALSE the list of existing islands is returned. Otherwise,
an object of class "spatial.neighbor" with remapped row.id and col.id.
SIDE EFFECTS:
the attribute "nregion" of x may be recomputed when remap=T.