Thank you, everyone!
Let me go walk through some of this, look at the help for some functions
that I haven't yet looked at, and see what I can make of it all! :-)
I let myself become trapped in a lab class with this issue... found that
the as.data.frame() worked fine on SpatialPoints, but ran into a problem
when someone asked to decompose a polygon similarly (I should have
looked before class, but ran out of time - too many commitments, not
enough time!).
Thank you again!
Pete
Roger Bivand wrote:
On Fri, 13 Feb 2009, Jim Burke wrote:
Hi Peter,
I think I am three days ahead of you on the learning curve. So come
join me! Below is a cumulation of suggestions from Rodger Bivand.
Perhaps the code below may help. Start out with your own
SpatialPolygon. Change it to a dataframe. Then do something data like
to the dataframe. Then coerce back to a SpatialPolygon dataframe.
Then dump the SpatialPolygon in various ways. Or you could simply
dump the SpatialPolygon. # the following code takes an sp to a df to
add the two columns
# then the df is coerced back into an sp. This solves a merge
# issue when merging an sp and df together. R thinks the result
# should be a data.frame so good bye SpatialPolygons
tx2_df <- as(tx2_sp, "data.frame") #make a sp into a df
tx2_df1 <- merge(tx2_df, votes2_df, sort=FALSE, by.x="PCT",
by.y="PCT", all.x=TRUE, all.y=TRUE)
remove(tx2_df)
remove(votes2_df)
# notice that the data frame row IDs we print are sequential
# 1,2,3,4... and not proper precinct names like 1234....
rownames(as(tx2_df1, "data.frame")) #show us the row IDs
Have you looked at spRbind and spChFIDs methods in maptools? I would
be worried about ignoring the IDs unless you are very confident that
the order of the geometric objects and the rows in the data frame are
identical. Since Peter mentioned our book, there is an extensive
example on pp. 120-126; the code and data are available in the Chapter
5 set on www.asdar-book.org, but without the explanations of the steps
involved.
Roger
# key here is match.ID = FALSE so that it does not try to take
# the 1,2,3 data frame sequence numbers and think they are IDs.
# both sp and df must have rows aligned the same.
tx3_sp <- SpatialPolygonsDataFrame(as(tx2_sp,"SpatialPolygons"),
data=tx2_df1, match.ID = FALSE)
remove(tx2_sp)
remove(tx2_df1)
# debug tx3_sp a little, lets make sure its a
SpatialPologonsDataFrame!
sapply(slot(tx3_sp, "polygons"), function(x) slot(x, "ID")) #what
are row "ID"s?
str(as(tx3_sp, "data.frame")) #show representation of
variables
(str(tx3_sp)) #shows representation of
geometries too.
names(tx3_sp) #nice but lengthy Let us know
if this helps you any.
Good luck,
Jim Burke
Peter S. Hayes wrote:
Hi All,
I'm trying to teach a spatial analysis class using R as a means of
learning some details... I'm not an expert in R myself, but am
learning it while using it as a 'tool' for lessons in the class...
In getting the students familiar with some of the SP classes, we
began looking at the class components and manipulating some of the
components (such as translating by modifying coordinates..).
Is there a means of decomposing SpatialPolygons to access the list
of Polygons and contained classes? The help files (for example,
polygons()) appear to hint so, but not function so... the
SpatialPolygons isn't quite a traditional R dataframe and won't
flatten with a call to as.data.frame() to allow access to the
individual slots... but there must be a means of doing that...
Also, I have "Applied Spatial Data Analysis with R" as one of the
texts... any thoughts for more references... especially for
non-programmers: I've some software experience (C/C++...) but most
of the students are environmental study, environmental science, or
biology students and this is one of their first experiences with
anything having a command line. We've been taking things slow, but R
is still a bit cryptic... any thoughts on that would be appreciated!
Thank you for all!
Pete
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