[R-sig-Geo] Complete neighbours

[Roger Bivand]

On Sun, 5 Sep 2010, German Sanchez Hernandez wrote:

> Dear Roger (and list):
>
> Thank you for your response. The idea to complete the neighbourhood list 
> is to try to "define" some regions using the features of their nearest 
> regions.
>
> I made a modification of union.nb function, once I've learned how to 
> edit the nb objects. I'll take a look on the nblag_cumul function.

Right, union.nb() is a better choice than nblag_cumul(), which is less 
general.

Roger

>
> Thanks and regards,
> German Sanchez
>
> El 05/09/2010, a las 21:14, Roger Bivand escribió:
>
>> On Fri, 3 Sep 2010, German Sanchez Hernandez wrote:
>>
>>> Dear list,
>>>
>>> I would like to complete my neighbour list in order to increase the number of neighbours of regions with less neighbours (links) than a certain number. The idea is to complete these links using knearneigh function.
>>>
>>>
>>> My try:
>>>
>>> nb <- poly2nb(map)
>>> # Compute distribution of linkage:
>>> distr <- as.data.frame(table(card(nb)))
>>> # Try to identify the "isolated" regions (equal or less than, for example, 3 neighbours
>>> minim <- 3 # It's a computed number
>>> isolated <- subset(nb, subset=card(nb) <= minim)
>>> # Get the "isolated" region IDs
>>> regions <- attr(unclass(isolated), 'region.id')
>>> # Modify nb using knearneigh ¿?
>>
>> For the edited version of nblag_cumul on R-forge on the spdep project, you'd do something like:
>>
>> example(columbus)
>> table(card(col.gal.nb))
>> k4 <- knn2nb(knearneigh(coordinates(columbus), 4))
>> mod_nb <- nblag_cumul(list(col.gal.nb, k4))
>> table(card(mod_nb))
>>
>> but I'm not at all sure that this is a good idea. Most often observations with few neighbours are on the edge of the data set, so there is a very good reason for their apparent "isolation".
>>
>> Hope this helps,
>>
>> Roger
>>
>>>
>>>
>>> # Alternative 2:
>>> nbmat <- nb2mat(nb)
>>> # Modify nbmat ¿?, mat2listw, listw2nb
>>>
>>>
>>> # Alternative 3:
>>> listw <- nb2listw(nb)
>>> # Modify listw ¿?, listw2nb
>>>
>>>
>>> The question is:
>>>
>>> How to modify nb (or nbmat or listw) to increase the number of links of the "isolated" regions?
>>>
>>> Any idea?
>>>
>>> Thank you!
>>> Germán Sánchez
>>> _______________________________________________
>>> R-sig-Geo mailing list
>>> R-sig-Geo at stat.math.ethz.ch
>>> https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>>>
>>
>> --
>> Roger Bivand
>> Economic Geography Section, Department of Economics, Norwegian School of
>> Economics and Business Administration, Helleveien 30, N-5045 Bergen,
>> Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
>> e-mail: Roger.Bivand at nhh.no
>
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>

-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand at nhh.no