adding ids and df to hexagonal polys ?

Thanks for the hints here... but I'm guessing that there's somethings
missing...

the 5th command line (row.names(o) <- row.names(hpoly)) does not make
sense to me as hpoly is a spatialPolygon which has no row names

str(hpoly,max.lev=2)

Formal class 'SpatialPolygons' [package "sp"] with 4 slots
  ..@ polygons   :List of 965
  ..@ plotOrder  : int [1:965] 1 2 3 4 5 6 7 8 9 10 ...
  ..@ bbox       : num [1:2, 1:2] 446230 3778428 1331230 8047934
  .. ..- attr(*, "dimnames")=List of 2
  ..@ proj4string:Formal class 'CRS' [package "sp"] with 1 slots

summary(row.names(hpoly))

Length  Class   Mode 
     0   NULL   NULL 

I thought, perhaps there's a spelling problem? but no...

row.names(o) <- row.names(hpoly)
hpoly1 <- SpatialPolygonsDataFrame(hpoly, data=o)

Error in SpatialPolygonsDataFrame(hpoly, data = o) : 
  row.names of data and Polygons IDs do not match

How is this possible?


So I tried a "brute force" approach, with no success

row.names(slot(cl,"polygons")) <- 1:length(slot(cl,"polygons"))

Error in `rownames<-`(x, value) : 
  attempt to set rownames on object with no dimensions

I seem to have the concept wrong to begin with here. How are IDs
assigned to a 'SpatialPolygons' class? I should be able to assign them
regardless of the template shape used, right? Which would make the
overlay() step unnecessary?


I guess that I need some clarification on how the class is built..
my apologies if it's too obvious of a  question... I just hope not to be
the only one missing this
 thanks

On Wed, 9 Sep 2009, Horacio Samaniego wrote:

Hi,

I am trying to understand the different data types in the sp package.
However, I do not seem to get the way that spdf are built.

For example, let say that I can build a hexagonal grid. That work just
fine using

regio <- readShapePoly("regions.shp")
hpts <- spsample(regio,type="hexagonal",cells=30000)
hpoly = HexPoints2SpatialPolygons(hpts)

I'm unclear about adding a df with IDs to this new SpetialPolygons class

library(maptools)
xx <- readShapePoly(system.file("shapes/sids.shp", package="maptools")[1],
  IDvar="FIPSNO", proj4string=CRS("+proj=longlat +ellps=clrk66"))
hpts <- spsample(xx, type="hexagonal", n=100)
hpoly <- HexPoints2SpatialPolygons(hpts)
o <- overlay(xx, hpts)
row.names(o) <- row.names(hpoly)
hpoly1 <- SpatialPolygonsDataFrame(hpoly, data=o)
summary(hpoly1)
spplot(hpoly1, "BIR74")

After making sure that the IDs agree, just use the constructor for
SpatialPolygonsDataFrame objects.

Hope this helps,

Roger

I guess that I'm not understanding how ids are assigned... any hint
would be appreciated

thanks

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