On Aug 5, 2010, at 2:48 PM, Archana Dayalu wrote:
Hello,
I am using read.table to read files directly from a public ftp site.
I have
a general list of files that may or may not exist in the ftp
directory, but
my hope was that R would read the file if it existed and ignored it
if it
didn't exist and move on to the next one. However, when R arrives at
a file
that does not exist I get the error message "Error in file(file,
"rt") :
cannot open the connection" This makes sense, but I was wondering if
there
was any way I could circumvent this error message and have R instead
give me
a warning message without terminating my entire loop.
Yes.
?try
Ideally, I would get a
warning message saying the connection does not exist, and then have
R skip
to the next file.
My code is copied below.
Something like these modifications .... untested:
hourly.years <- c(2000:2008)
hourly.species <- c('ch4','co2','co')
station.names <-
c
('alt482n00
','chm449n00
','egb444n01
','etl454n00','fsd449n00','llb454n01','wsa443n00','cdl453n00')
for (kk in hourly.years) {
for (i in hourly.species) {
for (nn in station.names) {
file1 <- paste('ftp://gaw.kishou.go.jp/pub/data/current/
',i,'/hourly/y',kk,'/',nn,'.ec.as.cn.',i,'.nl.hr',kk,'.anc',sep='')
#ancillary data
file2 <- paste('ftp://gaw.kishou.go.jp/pub/data/current/
',i,'/hourly/y',kk,'/',nn,'.ec.as.cn.',i,'.nl.hr',kk,'.dat',sep='')
#concentration data
dumm.anc <-
try( read.table(file1,skip=32,header=F,as.is=T) )
if (class(dumm.anc) == "try-error" {} else {
colnames(dumm.anc) <- c('DATE','TIME','WD','WS','RH','AT')
r.obj.anc <- paste(substr(nn,1,3),i,kk,'anc.cont',sep='.')
assign(r.obj.anc,dumm.anc)
}
dumm.dat <-
try( read.table(file2,skip=32,header=F,as.is=T) )
if (class(dumm.dat) == "try-error" {} else { #will skip over
following commands if "try-error-ed"
colnames(dumm.dat) <-
c('DATE','TIME','DATE','TIME','CH4','ND','SD','F','CS','REM')
r.obj.dat <- paste(substr(nn,1,3),i,kk,'dat.cont',sep='.')
assign(r.obj.dat,dumm.dat)
}
# --------------presumably these do not depend on the read-
tries---------
status<-paste(i,nn,kk,'----EC HOURLY/CONTINUOUS DAT/ANC
read
complete',sep=' ')
print(status,quote=F)
}
}
}
--
David Winsemius, MD
West Hartford, CT
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