[R] unexpected behavior from gzfile and unz

[Matthew Suderman]

I get unexpected behavior from "readLines()" and
"scan()" depending on how the file is opened with
"gzfile" or "unz".  More specifically:

> file <- gzfile("file.gz")
> readLines(file,1)
[1] "a\tb\tc"
> readLines(file,1)
[1] "a\tb\tc"
> close(file)

It seems that the stream is rewound between calls to
readLines.  The same is true if I replace readLines
with scan.

However, if I set argument 'open="r"', then rewinding
does not occur:

> file <- gzfile("file.gz",open="r")
> readLines(file,1)
[1] "a\tb\tc"
> readLines(file,1)
[1] "1\t2\t3"
> close(file)

Once again, I get the same behavior for scan.  The
rewinding behavior just described also appears if I
open a zip file with "unz".

> file <- unz("file.zip", "file.txt")
> readLines(file,1)
[1] "a\tb\tc"
> readLines(file,1)
[1] "a\tb\tc"
> close(file)

If I add the 'open="r"' argument to the call then I
get an error from readLines:

> file <- unz("file.zip", "file.txt", open="r")
> readLines(file,1)
Error in readLines(file, 1) : seek not enabled for
this connection
> close(file)


> file <- unz("file.zip", "file.txt", open="rb")
> readLines(file,1)
Error in readLines(file, 1) : seek not enabled for
this connection
> close(file)

However, if I instead use "scan" to read the file,
then there are no errors and I get the rewind/no
rewind behavior described above.

> file <- unz("file.zip", "file.txt")
> scan(file,nlines=1,sep="\t",what=character(0))
Read 3 items
[1] "a" "b" "c"
> scan(file,nlines=1,sep="\t",what=character(0))
Read 3 items
[1] "a" "b" "c"
> close(file)


> file <- unz("file.zip", "file.txt", open="r")
> scan(file,nlines=1,sep="\t",what=character(0))
Read 3 items
[1] "a" "b" "c"
> scan(file,nlines=1,sep="\t",what=character(0))
Read 3 items
[1] "1" "2" "3"
> close(file)

Is this a bug?

Matt



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