Hi Mark,
This question would probably be better suited for the r-sig-geo mailing
list. In addition, please read the posting guide and provide a piece of
code that reproduces the problem.
library(sp)
convert<-function(d) {
d<-data.frame(d); #convert object to dataframe
d<-subset(d,select=c(zinc,x,y)) #select some columns
d # <- add this, or alternatively 'return(d)'
}
data(meuse)
coordinates(meuse) = ~x+y
convert(meuse)
But maybe better, subsetting a SPDF can be done using:
meuse["zinc"] # Remains an SPDF
# Returns a data.frame
data.frame(coordinates(meuse), zinc = meuse$zinc)
And some unrequested advice :). To process multiple files, take a look
at lapply, both for reading and processing.
all_data = lapply(list_of_files, function(file) {
bla = read.table(file)
coordinates(bla) = ~coor.x1 + coor.x2
return(bla)
}
# all data is now a list wit the SPDF's
processed_data = lapply(all_data, function(dat) {
return(data.frame(coordinates(dat), zinc = dat$zinc))
}
ofcourse you can include the latter lapply stuff inside the first
'loading' lapply.
all_data = lapply(list_of_files, function(file) {
bla = read.table(file)
bla = subset(bla, select = select=c(time,coords.x1,coords.x2))
coordinates(bla) = ~coor.x1 + coor.x2
return(bla)
}
hope this helps and good luck,
Paul
Mark Na wrote:
Hello,
I am learning how to use functions, but I'm running into a roadblock.
I would like my function to do two things: 1) convert an object to a
dataframe, 2) and then subset the dataframe. Both of these commands work
fine outside the function, but I would like to wrap them in a function so I
can apply the code iteratively to many such objects.
Here's what I wrote, but it doesn't work:
convert<-function(d) {
d<-data.frame(d); #convert object to dataframe
d<-subset(d,select=c(time,coords.x1,coords.x2)) #select some columns
}
convert(data) #the problem is that "data" is the same as it was before
running the function
The objects being processed through my function are SpatialPointsDataFrames
but I'm quite sure that's not my problem, as I can process these outside of
the function (using the above code) ... it's when I try to wrap the code in
a function that it doesn't work.
Thanks, Mark
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--
Drs. Paul Hiemstra
Department of Physical Geography
Faculty of Geosciences
University of Utrecht
Heidelberglaan 2
P.O. Box 80.115
3508 TC Utrecht
Phone: +3130 274 3113 Mon-Tue
Phone: +3130 253 5773 Wed-Fri
http://intamap.geo.uu.nl/~paul
______________________________________________
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
