[R] read.csv returns "no lines available for input"

Collins, Stephen
Fri, 18 Jan 2013 20:26:14 -0000

Hello,

I'm trying to read a file rows at a time, so as to not read the entire file
into memory.  When reading the connections and readLines help, and R help
archive, it seems this should be possible with read.csv and a file connection,
making use of the "nrows" argument.

>From certain posts, it seemed that read.csv should return
"character(0)" when the end of file is reached, and there are no more
rows to read.  Instead, I get an error there are "no lines available for
input."

What is the proper way to check the end-of-file condition with read.csv, such
that I could break a while loop reading the data in?

#example, make a test file
con <- file("test.csv","wt")
cat("a,b,c\n", "1,2,3\n", "4,5,6\n",
"7,6,5\n", "4,3,2\n", "3,2,1\n",file=con)
unlink(con)

#show the file is valid
con <- file("test.csv","rt")
read.csv(con,header=T)
unlink(con)

#show that readLines ends with "character(0)", like expected
con <- file("test.csv","rt")
readLines(con,n=10)
readLines(con,n=10)
unlink(con)

#show that read.csv end with error
con <- file("test.csv","rt")
read.csv(con,header=T,nrows=10)
read.csv(con,header=F,nrows=10)
unlink(con)



Sincerely,

Stephen


> sessionInfo()
R version 2.15.0 (2012-03-30)
Platform: i386-pc-mingw32/i386 (32-bit)

locale:
[1] LC_COLLATE=English_United States.1252
[2] LC_CTYPE=English_United States.1252
[3] LC_MONETARY=English_United States.1252
[4] LC_NUMERIC=C
[5] LC_TIME=English_United States.1252

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base

loaded via a namespace (and not attached):
[1] tools_2.15.0


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