[R] Using files as connections

[Liaw, Andy]

You are using the connection the wrong way.  You need to do something like:

fcon <- file("c:/data/perry/data.csv", open="r")
for (iline in 1:slines) {
    isel <- isel + 1
    cline <- readLines(fcon, n=1)
    ...
}
close(fcon)

BTW, here's how I'd do it (not tested!):

strvec <- rep("",slines)
selected <- sort(sample(flines, slines))
skip <- c(0, diff(selected) - 1)
fcon <- file("c:/data/[erry/data.csv", open="r")
for (i in 1:length(skip)) {
    ## skip to the selected line
    readLines(fcon, n=skip[i])
    strvec[i] <- readLines(fcon, n=1)
}
close(fcon)

HTH,
Andy


> -----Original Message-----
> From: maj at stats.waikato.ac.nz [mailto:maj at stats.waikato.ac.nz] 
> Sent: Wednesday, August 27, 2003 7:19 PM
> To: r-help at stat.math.ethz.ch
> Subject: [R] Using files as connections
> 
> 
> I have been trying to read a random sample of lines from a 
> file into a data frame using readLines(). The help indicates 
> that readLines() will start from the current line if the 
> connection is open, but presented with a closed connection it 
> will open it, start from the beginning, and close it when finished.
> 
> In the code that follows I tried to open the file before 
> reading but apparently without success, because the result 
> was repeated copies of the first line:
> 
> flines <- 107165
> slines <- 100
> selected <- sort(sample(flines,slines))
> strvec <- rep("",slines)
> file("c:/data/perry/data.csv",open="r")
> isel <- 0
> for (iline in 1:slines) {
>   isel <- isel + 1
>   cline <- readLines("c:/data/perry/data.csv",n=1)
>   if (iline == selected[isel]) strvec[isel] <- cline else
>     isel <- isel - 1
> }
> close("c:/data/perry/data.csv")
> sel.flows <- read.table(textConnection(strvec), header=FALSE, sep=",")
> 
> 
> There was also an error "no applicable method"  for close.
> 
> Comments gratefully received.
> 
> Murray Jorgensen
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list 
> https://www.stat.math.ethz.ch/mailman/listinfo> /r-help
> 

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