[R] Writing output of a looped process with pdfs

[Larrosa, Cecilia]

Hi,

I have created a list of spdfs, and I am looping a process for each of them. The process is using dDistance to calculate distances between features within each spdf. I want to write the output tables using the name of the spdf at each loop, but cannot find a way to do this. It seems a rather basic thing to do, and I am not very proficient in R, but I have spent several hours looking for a way to do this and failed. I am using R studio on a Mac.

Here is the code so far (not the most efficient code):

# Load libraries
library(rgdal)
library(gdistance)

#Read forest shape files
setwd("/Users/sisolarrosa/Documents/PhD/R_work/AF/IIC/split_fnp/")
shps<- dir(getwd(), "*.shp")
shps <- gsub('.{4}$', '', shps)
for (shp in shps) assign(shp, readOGR(".",layer=shp))

#Create list (I did this manually because I could not find another way)
fnps <- list(a_1, a_10, a_100, a_101, a_102, a_103, a_104, a_105, a_106, a_107, a_108, a_109, a_11, a_110,
             a_111, a_112, a_113, a_12, a_13, a_14, a_15, a_16, a_17, a_18, a_19, a_2, a_20, a_21, a_22, a_23,
             a_24, a_25,  a_26, a_27,  a_28, a_29, a_3, a_30, a_31, a_32, a_33, a_34, a_35, a_36, a_37,
             a_38, a_39, a_4, a_42, a_43, a_44, a_45, a_46, a_47, a_48, a_49, a_5, a_50, a_51, a_52,
             a_53, a_54, a_55,  a_56, a_57, a_6,  a_69, a_7, a_70,  a_73, a_79, a_8,  a_80, a_81, a_82,
             a_83,  a_84, a_85, a_86, a_87, a_88, a_89, a_9,  a_90, a_91, a_94, a_95, a_96, a_98, a_99)


###  Calculate distance between all polygons
for (fnp in fnps)
{
  distance.matrix<- gDistance(fnp, spgeom2= NULL, byid=T);
  row.names(distance.matrix) <- paste(1:nrow(distance.matrix), sep="”);# did this because gDistance changed the IDs of the features from [1 to ...] to [0 to ...], not sure why
  colnames(distance.matrix)<- paste(1:ncol(distance.matrix), sep="”); # same as above
  dists.melt <- melt(distance.matrix)[melt(upper.tri(distance.matrix))$value,]; #use only lower triangle of the distances matrix
  outfile <- file.path("/Users/sisolarrosa/Documents/PhD/R_work/AF/IIC/conefor_inputs/", paste0("distances_", fnp, ".txt")); # this is the bit that is not working
  write.table(dists.melt, outfile,row.names=FALSE, col.names=FALSE)
}

And this is the error message:

Error in as.character.default(<S4 object of class "SpatialPolygonsDataFrame">) :
  no method for coercing this S4 class to a vector

Can anyone help me with solving the issue? How to call the name of the looped spdf to be included in the title of the output table? I really appreciate your time!

Cheers
Cecilia


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