testnb: Test a neighbours list for symmetry

Description Usage Arguments Value Note Author(s) See Also Examples

Description

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.

Usage

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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.

Author(s)

Roger Bivand [email protected]

See Also

read.gal

Examples

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if (require(rgdal, quietly=TRUE)) {
example(columbus, package="spData")
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))
}

spdep documentation built on Nov. 21, 2018, 5:05 p.m.