[R-sig-Geo] Merging shapefiles and csv

[Lyndon Estes]

I am not sure about the mismatch issue, but I thinking merging the
data slot of spatialPolygonsDataFrame with a data frame produces
undesirable results.

I wrote a function a while back that does the merge in such a way that
the problems are avoided, and perhaps this might help.  I think there
are other, more recent, and undoubtedly better solutions (in fact I
recall seeing a very recent thread about this, but not sure where)
than this one that you could find.

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 update x2 into a data.frame
  row.names(x.dat2.ord) <- row.names(x2.dat)  # Reassign row.names
from original data.frame
  x2 at data <- x.dat2.ord  # Assign to shapefile the new data.frame
  return(x2)
}

Hope it helps.

Best, Lyndon


On Thu, Jul 31, 2014 at 8:32 AM, HallS <sam_l_cruickshank at hotmail.com> wrote:
> Hi all,
>
> I'm struggling to know how this will come across as my data is confidential.
>
> Basically I have a shapefile (.shp) and a csv file while contain the same
> regions (i.e.) a column which has the same information.  Using this link:
> https://sites.google.com/site/eospansite/alobotips/spatial_r_tips/rshp_xls
> I managed to get quite far but once I got to the writeOGR command, I get the
> error
>  Error in writeOGR(RSANHS, dsn = "C:/Users/Laptop/Documents/Rworkspace/",  :
>   number of objects mismatch
>
> shape1 at data <- merge(shape1 at data,csv,by.x="RSA",
> +                           by.y="RSA", all.x=T, sort=F)
>>
>> ###Checking it
>> dim(shape at data)
> [1] 1745    2
>> dim(shape1 at data)
> [1] 1747    5
>
> This shows a discrepancy in two rows between the original shapefile and the
> new merged one.  When I looked at the merged file in full, there were a
> number of NA rows at the bottom where there was no corresponding data to the
> shapefile.  I tried shape1 at data <- na.exclude(shape1 at data) and with na.omit,
> and this did reduce the number of rows to 1690, but the problem persists.
>
> Sorry if this is a really unhelpful question, I'm not sure how to do it when
> data is confidential.
>
>
>
> --
> View this message in context: http://r-sig-geo.2731867.n2.nabble.com/Merging-shapefiles-and-csv-tp7586839.html
> Sent from the R-sig-geo mailing list archive at Nabble.com.
>
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