is.symmetric.nb

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Test a neighbours list for symmetry

Checks a neighbours list for symmetry/transitivity (if i is a neighbour of j, then j is a neighbour of i). This holds for distance and contiguity based neighbours, but not for k-nearest neighbours. The helper function sym.attr.nb() calls is.symmetric.nb() to set the sym attribute if needed, and make.sym.nb makes a non-symmetric list symmetric by adding neighbors. is.symmetric.glist checks a list of general weights corresponding to neighbours for symmetry for symmetric neighbours.

Keywords
spatial
Usage
is.symmetric.nb(nb, verbose = NULL, force = FALSE) sym.attr.nb(nb) make.sym.nb(nb) old.make.sym.nb(nb) is.symmetric.glist(nb, glist)
Arguments
nb
an object of class nb with a list of integer vectors containing neighbour region number ids.
verbose
default NULL, use global option value; if TRUE prints non-matching pairs
force
do not respect a neighbours list sym attribute and test anyway
glist
list of general weights corresponding to neighbours
Value

TRUE if symmetric, FALSE if not; is.symmetric.glist returns a value with an attribute, "d", indicating for failed symmetry the largest failing value.

Note

A new version of make.sym.nb by Bjarke Christensen is now included. The older version has been renamed old.make.sym.nb, and their comparison constitutes a nice demonstration of vectorising speedup using sapply and lapply rather than loops. When any no-neighbour observations are present, old.make.sym.nb is used.

See Also

read.gal

Aliases
  • is.symmetric.nb
  • sym.attr.nb
  • make.sym.nb
  • old.make.sym.nb
  • is.symmetric.glist
Examples
example(columbus)
coords <- coordinates(columbus)
ind <- sapply(slot(columbus, "polygons"), function(x) slot(x, "ID"))
print(is.symmetric.nb(col.gal.nb, verbose=TRUE, force=TRUE))
k4 <- knn2nb(knearneigh(coords, k=4), row.names=ind)
k4 <- sym.attr.nb(k4)
print(is.symmetric.nb(k4))
k4.sym <- make.sym.nb(k4)
print(is.symmetric.nb(k4.sym))
Documentation reproduced from package spdep, version 0.6-9, License: GPL (>= 2)

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