[R-sig-Geo] Spatial Query (Selection) with Apply

[Ariel Fuentesdi]

Thanks, Robin

It worked perfectly, although I transformed the data from sf to
SpatialDataFrame objects with:

zones <- as(zones, "Spatial")
nodes <- as(nodes, "Spatial")

The next step I will follow is to create Distance Matrix like this:

coord <- tmp2[[1]]@coords
dist1 <- apply(X = coord, MARGIN = 1, FUN = function(x) spDistsN1(coord, x,
longlat = T))

obviously, the task is a distance matrix for every selection. ¿What would
you recommend, the aggregate function as you talked before or something
like a nested apply?

Regards,
Ariel



2018-08-27 19:32 GMT-03:00 Robin Lovelace <rob00x using gmail.com>:

> Hi Ariel,
>
> It helps when asking for help with code to produce a reproducible example.
> To understand your input data I've created nodes and zones based on the
> spData data nz_height and nz_elev. Based on the assumption you want to find
> all the nodes in each zone I think the direct answer to your question is
> something like the following:
>
> tmp2 = lapply(s, function(x) {
>   nodes[zones[x, ], ]
> })
>
> The longer answer is that aggregate(), st_join() + aggregate()/summarize()
> may provide quicker solutions, depending on what you want to do with the
> points after grouping them by which zone they fall in.
> Note: I've used sf objects based on the explanation here
> https://geocompr.robinlovelace.net/spatial-operations.html#spatial-vec
> which may not work with sp data but the aggregate code should work roughly
> the same:
>
> # install.packages("sf")
> # install.packages("spData")
> library(spData)
> library(sf)
> #> Linking to GEOS 3.6.2, GDAL 2.2.3, proj.4 4.9.3
> zones = nz
> nodes = nz_height
> tmp = list()
> s = 1:nrow(nz)
>
> for(i in s) {
>   tmp[[i]] = nodes[nz[i, ], ]
> }
>
> # understand what's going on with plots (not shown)
> # plot(st_geometry(nz))
> # plot(st_geometry(tmp[[i]]), add = TRUE, col = "red")
> # plot(nz[i, ], col = "green", add = TRUE)
>
> tmp2 = lapply(s, function(x) {
>   nz_height[nz[x, ], ]
> })
>
> identical(tmp, tmp2)
> #> [1] TRUE
>
> Created on 2018-08-27 by the [reprex package](http://reprex.tidyverse.org)
> (v0.2.0).
>
> I've also pasted the reprex into the geocompr github tracker so the plots
> can be seen and the code formatted: https://github.com/Robinlovela
> ce/geocompr/issues/294
>
> Hope this helps,
>
> Robin
>
>
> On Mon, Aug 27, 2018 at 9:53 PM, Ariel Fuentesdi <ariel.fuentesdi using usach.cl
> > wrote:
>
>> Hi,
>>
>> I want to do multiple selections of a point shapefile based on polygons on
>> other layers, I can do this in a for loop, but I desire to do this in a
>> function of the apply family.
>>
>> I named the point shapefile "nodes" and the polygons shapefile "zones".
>>
>> This is what I did:
>>
>> tmp <- list()
>> for (i in 1:nrow(zones using data)) {
>>     tmp[[i]] <- nodes[subset(zones, ESTUDIO == i),]
>>     tmp
>>   }
>>
>> But I have no clue how to change it to the apply family, can you provide
>> an example of this?
>>
>> Thanks in advance.
>>
>> Regards,
>> Ariel Fuentes
>>
>>         [[alternative HTML version deleted]]
>>
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>
>

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