[R-sig-Geo] Counting points within polygons

[Edzer Pebesma]

Agus,

Have you looked into "over", which is supposed to replace overlay?

require(sp)
vignette("over")

On 10/18/2011 05:06 PM, Agustin Lobo wrote:
> Actually, neither alternative works if there are polygons with no
> points, as those
> are not kept in the output of overlay and just binding tp the table of
> srdf is not possible.
>
> The second alternative looks easier for a join, but a problems comes
> from the fact that
> the output data.frame of
> delme4<- overlay(meuse2[,13],srdf,fn=sum)
>
> has different row.names than that of the input srdf:
>> row.names(srdf)
> [1] "r1" "r2" "r3"
>> delme4<- overlay(meuse2[,13],srdf,fn=sum)
>> row.names(delme4)
> [1] "X1" "X2" "X3"
>
> which is inconvenient, as the way to join delme4 to srdf would be
> using the row.names.
>
> Agus
>
>
> 2011/10/18 Agustin Lobo<alobolistas at gmail.com>:
>> Hi!
>>
>> Given a Sp Points DF and an Sp Polygons DF, I want to add a field of
>> number of points for each polygon
>> to the Sp Pol. DF table. This is what I'm doing (using objects from
>> the help page for sp::overlay()
>> (meuse is the Sp Points DF and srdf the Sp Pol. DF)
>>
>>> delme3<- overlay(meuse,srdf)
>>> delme3
>>   [1] 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
>>   [38] 1 1 1 1 1 1 2 1 2 2 2 2 2 2 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3
>>   [75] 3 3 3 3 3 3 3 3 2 1 2 2 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 2 2 2 2 2 2 2 2 2
>> [112] 2 2 2 2 2 2 3 2 2 2 2 2 1 2 2 2 2 1 1 2 2 1 2 2 2 2 3 3 3 3 3 3 3 3 3 3 3
>> [149] 3 3 3 3 3 3 3
>> newdata<- data.frame(srdf at data,nppoints=table(delme3))
>> srdf2<- srdf
>> srdf2 at data<- newdata
>>
>> An alternative:
>> newdatap<- data.frame(meuse at data, nbp=rep(1,nrow(meuse)))
>> meuse2<- meuse
>> meuse2 at data<- newdatap
>> delme4<- overlay(meuse2[,13],srdf,fn=sum)
>> newdata<- data.frame(srdf at data,nppoints=delme4)
>> srdf2<- srdf
>> srdf2 at data<- newdata
>>
>> I wonder if there is a better way or, best, an standard R spatial
>> function doing that already.
>>
>> Thanks!
>>
>> Agus
>>
>
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-- 
Edzer Pebesma
Institute for Geoinformatics (ifgi), University of Münster
Weseler Straße 253, 48151 Münster, Germany. Phone: +49 251
8333081, Fax: +49 251 8339763  http://ifgi.uni-muenster.de
http://www.52north.org/geostatistics      e.pebesma at wwu.de