Lyndon —
I couldn't figure out how to get x2 out of the function and into my workspace
so I could save it as a shapefile. I instead converted your code into a script
to run it, and it works like a charm. Thanks very much!
Sam
On Nov 2, 2011, at 12:27 PM, Lyndon Estes wrote:
> Hi Sam,
>
> I wrote the following function a while ago to account for this problem
> of dataframe row reordering relative to the polygon IDs:
>
> joinAttributeTable <- function(x, y, xcol, ycol) {
> # Merges data frame to SpatialPolygonsDataFrame, keeping the correct
> order. Code from suggestions at:
> # https://stat.ethz.ch/pipermail/r-sig-geo/2008-January/003064.html
> # Args:
> # x: SpatialPolygonsDataFrame
> # y: Name of data.frame to merge
> # xcol: Merge column name
> # ycol: Merge column name
> # Returns: Shapefile with merged attribute table
>
> x$sort_id <- 1:nrow(as(x, "data.frame")) # Column containing
> original row order for later sorting
>
> x.dat <- as(x, "data.frame") # Create new data.frame object
> x.dat2 <- merge(x.dat, y, by.x = xcol, by.y = ycol) # Merge
> x.dat2.ord <- x.dat2[order(x.dat2$sort_id), ] # Reorder back to original
> x2 <- x[x$sort_id %in% x.dat2$sort_id, ] # Make new set of polygons,
> dropping those which aren't in merge
> x2.dat <- as(x2, "data.frame") # Make updated x2 into a data.frame
> row.names(x.dat2.ord) <- row.names(x2.dat) # Reassign row.names from
> original data.frame
> x2@data <- x.dat2.ord # Assign to shapefile the new data.frame
> return(x2)
> }
>
> I haven't used this in a while, so I hope it still works. I think
> others could suggest a more efficient, existing method for dealing
> with this as well.
>
> Cheers, Lyndon
>
>
> On Wed, Nov 2, 2011 at 12:12 PM, Sam Rabin <sra...@princeton.edu> wrote:
>> Hello!
>>
>> I have a shapefile (.shp) containing the Landsat grid coverage of South
>> America. I also have 97 other shapefiles, each of which covers one of the
>> Landsat grid cells (the 97 being a subset of the cells in the first
>> shapefile). I managed to get R (via maptools) to perform a calculation on
>> each of the 97 and put the results in a data frame. Among other things, this
>> data frame contains a column for grid cell ID that matches up with a column
>> in the Landsat grid shapefile. I used merge() to combine these and then
>> saved a new shapefile, following the instructions at
>> http://help.nceas.ucsb.edu/R:_Spatial#Append_a_second_set_of_attributes_to_a_spatial_data_file.27s_attribute_table.
>> Here is the code I used:
>>
>> require(maptools)
>> landsat1 = readShapePoly("landsat_grid")
>> # Make a backup
>> landsat_orig = landsat1
>> landsat_2_spdf =
>> merge(landsat1@data,newcalc,by.x="PR",by.y="pr2",all.x=TRUE,sort=FALSE)
>> landsat1@data = landsat_2_spdf
>> writeSpatialShape(landsat1, "methodA")
>>
>> Looking at the new data with
>>
>> View(landsat1@data),
>>
>> it seemed like everything went great. The ID's matched up perfectly, and I
>> checked some of the calculated figures and they matched, too. The polygons
>> from landsat_grid.shp that were not included in the 97 were assigned NA for
>> the column with the calculated figures, appropriately.
>>
>> Unfortunately, when I imported the new shapefile to my GIS program, all the
>> tiles were rearranged. screenshot_expectedcoverage
>> (http://tinyurl.com/3nbm3q7 ) shows fine-scale data for what I was expecting
>> (Amazonia; imagine a polygon drawn around all the data there), and
>> screenshot_methodA (http://tinyurl.com/3htvlga) shows what I got. (Only the
>> 97 polygons are shown.)
>>
>> I tried changing sort to TRUE in the fourth line (and the output shapefile
>> name to "methodB"), but the tiles are still messed up, just differently —
>> see screenshot_methodB (http://tinyurl.com/3h95vr3).
>>
>> In both shape files, the attribute tables look fine, but the tiles are just
>> totally rearranged. They're not all scattered over the world, either. In
>> screenshot_rearrangement (which shows all tiles, not just the 97)
>> (http://tinyurl.com/6xfabvm), you can see that they cover South America
>> perfectly — they all line up with the polygons from landsat_grid.shp (not
>> shown).
>>
>> What do I need to do to fix this?
>>
>> Thanks very much in advance.
>>
>>
>>
>> Sam Rabin
>> Graduate student
>> Princeton University
>> Ecology & Evolutionary Biology
>>
>>
>>
>>
>>
>>
>> [[alternative HTML version deleted]]
>>
>>
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>>
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