How to read multiple .gpx files in R [closed]

Question

Suppose I have a number of .gpx files (these contain GPX waypoint data from a Garmin eTrex). I want to load them into R with different names and manipulate them.

I can read one file thus:

library(maptools)
gpx.raw <- readGPS(i = "gpx", f = "file1_w_12_f_ddf.gpx", type="w")

Suppose I want to read a number of them into memory. I could try a for loop:

files <- list.files(".",pattern = "*.gpx")
for(x in files){

    #Create new file name
    temp <- strsplit(x,"_",fixed=TRUE)
    visit.id <- sapply(temp,FUN=function(x){paste(x[1],x[4],substr(x[5],1,3),sep="_")})

    #read file with new filename
    assign(visit.id, readGPS(i = "gpx", f = x, type="w"))
}

Running above program yields following error:

Error in read.table(con <- textConnection(gpsdata), fill = TRUE, ...) : no lines available in input In addition: Warning message: running command 'C:\PROGRA~2\GPSBabel\gpsbabel.exe -w -i gpx -f file1_w_12_f_ddf.gpx -o tabsep -F -' had status 1

Note that I was able to read this file on its own, so it would seem it has nothing to do with the file itself but with running readGPS in a loop.

In general I still find it very confusing how R treats variables like x above. I am not sure how to modify the argument to readGPS from the stand alone instance f = "file1_w_12_f_ddf.gpx": Should it be x, or f = x, or f = "x", or what? Or maybe the problem is in the call to GPSBabel...

I include a sample file below so you can copy it to text editor, and save as .gpx. twice with different names and try yourself.

<?xml version="1.0" encoding="UTF-8"?>
<gpx
 version="1.0"
 creator="GPSBabel - http://www.gpsbabel.org"
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xmlns="http://www.topografix.com/GPX/1/0"
 xsi:schemaLocation="http://www.topografix.com/GPX/1/0 http://www.topografix.com/GPX/1/0/gpx.xsd">
 <time>2010-09-14T18:35:43Z</time>
 <bounds minlat="18.149888897" minlon="-96.747799935" maxlat="50.982883293" maxlon="121.640266674"/>
<wpt lat="38.855549991" lon="-94.799016668">
<ele>325.049072</ele>
 <name>GARMIN</name>
 <cmt>GARMIN</cmt>
 <desc>GARMIN</desc>
 <sym>Flag</sym>
 </wpt>
 <wpt lat="50.982883293" lon="-1.463899976">
 <ele>35.934692</ele>
 <name>GRMEUR</name>
 <cmt>GRMEUR</cmt>
 <desc>GRMEUR</desc>
 <sym>Flag</sym>
 </wpt>
 <wpt lat="25.061783362" lon="121.640266674">
 <ele>38.097656</ele>
 <name>GRMTWN</name>
 <cmt>GRMTWN</cmt>
 <desc>GRMTWN</desc>
 <sym>Flag</sym>
 </wpt>
 </gpx>

Answer 1

I can't say why it is not working with the readGPS function in the maptools package, but I was able to loop through the files reading in the data using the readOGR function in the rgdal package.

setwd("C:\\Documents and Settings\\Owner\\Desktop\\R_test")
library(rgdal)   

#I just saved my text files in the above directory
myfiles <- list.files()

#this works, note track_points on layer name does not work!
gpx.raw <- readOGR(dsn = myfiles[1], layer="waypoints")

#now making function
for (i in 1:3) {
temp.gpx <- readOGR(dsn = myfiles[i], layer="waypoints")
temp.gpx
}