Re: [R] merge and polylist

From: Mihai Nica <mihainica_at_yahoo.com>
Date: Mon 09 Oct 2006 - 16:36:37 GMT


Thanks! I believe I have all I need to solve my issue.

Thank you very, very much,

mihai

On Mon, 9 Oct 2006, Mihai Nica wrote:

> The answer to all your questions is simple. By the time I get a little
> grasp on things, they become "deprecated" :-). But my programming skills
> are so low, that I find this normal.

> My problem comes from the last two #comment lines :

> #(if data row names do not match polygon IDs, will reorder, or fail if
> # any differ or absent

> The two data row names differ and some are absent, that's why I used
> "merge" (and posted on this list, not on r-sig-geo :-)). How else can I
> intersect the two data.frames?

Yes, use merge, but do look carefully at both of the input data frames, the by.x= and by.y= columns, and the output data frame. The sp classes give an ID to each polygon:

sapply(slot(object, "polygons"), function(x) slot(x, "ID"))

and that has to be identical to the row names of the output data frame - but can be in a different order. Constructing the SpatialPolygonsDataFrame will put the data frame rows in the order of the polygons.

Roger

> Thanks so much for your help!

On Sat, 7 Oct 2006, Mihai Nica wrote:

> Greetings:
>
> I would like to kindly ask for a little help. The rough code is:
>

Maybe R-sig-geo would be a more relevant list. Comments inline.

> #________________________________________________________
>
> dat=data.frame(read.delim(file="all.txt", header = TRUE, sep = "\t",
> quote="\"", dec=".",na.strings = "NA"))

We do not know if dat is in the same order as the shapefile. If dat$cod is malformed wrt. nc$att.data$AREA (very strange choice, in ESRI generated files often the polygon area), you are asking for trouble.

>
> nc=read.shape("astae.shp", dbf.data=TRUE, verbose=TRUE)
>
> mappolys=Map2poly(nc)
>
> submap <- subset(mappolys, nc$att.data$NAME!="Honolulu, HI")
>
> nc$att.data=subset(nc$att.data, nc$att.data$NAME!="Honolulu, HI")
>

In situations like this, overwriting the input is not advisable, bercause you destroy your ability to check that the output corresponds to your intentions.   

> nc$att.data[,1]=as.numeric(paste(nc$att.data$MSACMSA))
>
> #attributes(nc$att.data)
>
> nc$att.data=merge(nc$att.data, dat, by.x="AREA", by.y="cod", all.x=TRUE,
> sort=FALSE)

Ditto.

>
> #attributes(nc$att.data)
>
> tmp=file("tmp")
>
> write.polylistShape(submap, nc$att.data, "tmp")
>

Any good reason for not using the sp class framework? The objects you are using here are very low-level and messy.

library(maptools)
nc_1 <- readShapePoly(system.file("shapes/sids.shp", package="maptools")[1],   ID="FIPS") # put shapefile in SpatialPolygonsDataFrame nc_2 <- nc_1[coordinates(nc_1)[,1] < -80,] # subset with "[" method row.names(as(nc_2, "data.frame"))
as.character(nc_2$FIPS)
tmpfl <- paste(tempfile(), "dbf", sep=".") download.file("http://spatial.nhh.no/misc/nc_xtra.dbf";;, tmpfl, mode="wb") nc.df <- read.dbf(tmpfl) # extra data keyed on CNTY_ID nc_2$CNTY_ID
nc.df$CNTY_ID
nc_df2 <- merge(as(nc_2, "data.frame"), nc.df, by="CNTY_ID", sort=FALSE) all.equal(nc_df2$CNTY_ID, nc_2$CNTY_ID)
row.names(nc_df2) <- nc_df2$FIPS # re-instate IDs nc_3 <- SpatialPolygonsDataFrame(as(nc_2, "SpatialPolygons"), data=nc_df2) # (if data row names do not match polygon IDs, will reorder, or fail if # any differ or absent
writePolyShape(nc_3, "nc_3")

This still isn't as tidy as it could be, but gives much more control than the original old-style classes.

Roger

> #_________________________________________________________
>
> All works fine, but merge() changes the rownames and the link between the
> polygons and the corresponding rows is lost. I tried numerous other
> solutions (such as to "paste" back the old rownames), to no avail. After a
> few days, here I am. Please, if you have a moment, send a tip.
>
> Thanks,
>
> mihai
>
>
>

-- 
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@nhh.no

______________________________________________
R-help@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.








-- 
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@nhh.no








	[[alternative HTML version deleted]]

______________________________________________
R-help@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
Received on Tue Oct 10 02:41:13 2006

Archive maintained by Robert King, hosted by the discipline of statistics at the University of Newcastle, Australia.
Archive generated by hypermail 2.1.8, at Mon 09 Oct 2006 - 17:30:09 GMT.

Mailing list information is available at https://stat.ethz.ch/mailman/listinfo/r-help. Please read the posting guide before posting to the list.