[R] readLines() and unz() and non-empty final line

[Marttila Mikko]

Hi Kimmo,

Thanks, scan() does indeed seem to work for just reading lines, at least with the following options:

    scan(what = character(), sep = "\n", na.strings = "", quiet = TRUE)

However, I can't say I'm confident I didn't forget some option for an edge case; and it's a bit of a mouthful.

Is it possible to somehow use unzip() with connections? My understanding is that it just creates files on disk in the given output directory. I'm using unz() because I don't want that.

Best,

Mikko

-----Original Message-----
From: R-help <r-help-bounces using r-project.org> On Behalf Of Kimmo Elo
Sent: Friday, 25 October 2024 15:21
To: r-help using r-project.org
Subject: Re: [R] readLines() and unz() and non-empty final line

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Hi,

you could use "scan" instead, it seems to work fine also when wrapped around "unz".

Or, alternatively, you could use "unzip" instead of "unz". It works as expected, i.e. reads the last incomplete line and throws a warning about this.

So it seems to me that "unz" creates a non-blocking connection, whereas "unzip" creates a blocking connection. But this is a pure guess based on how the behave :-)

Best,

Kimmo

Bert Gunter kirjoitti 24.10.2024 klo 20.12:
> But note:
>
>> zip("hello.zip", "hello.txt")
> updating: hello.txt (stored 0%)
>> readChar(unz("hello.zip","hello.txt"),100)
> [1] "hello"
>
> I leave it to you and other wiser heads to figure out.
>
> Cheers,
> Bert
>
> On Thu, Oct 24, 2024 at 8:57 AM Iris Simmons <ikwsimmo using gmail.com> wrote:
>
>> Hi Mikko,
>>
>>
>> I tried running a few different things, and it seems as though
>> explicitly using `open()` and opening a blocking connection works.
>>
>> ```R
>> cat("hello", file = "hello.txt")
>> zip("hello.zip", "hello.txt")
>> local({
>>      conn <- unz("hello.zip", "hello.txt")
>>      on.exit(close(conn))
>>      ## you can use "r" instead of "rt"
>>      ##
>>      ## 'blocking = TRUE' is the default, so remove if desired
>>      open(conn, "rb", blocking = TRUE)
>>      readLines(conn)
>> })
>> ```
>>
>> A blocking connection might be undesirable for you, in which case
>> someone else might have a better solution.
>>
>> On Thu, Oct 24, 2024 at 10:58 AM Marttila Mikko via R-help
>> <r-help using r-project.org> wrote:
>>>
>>> Dear list,
>>>
>>> I'm seeing a strange interaction with readLines() and unz() when
>>> reading a file without an empty final line. The final line gets dropped silently:
>>>
>>>> cat("hello", file = "hello.txt")
>>>> zip("hello.zip", "hello.txt")
>>>    adding: hello.txt (stored 0%)
>>>> readLines(unz("hello.zip", "hello.txt"))
>>> character(0)
>>>
>>> The documentation for readLines() says if the final line is
>>> incomplete
>> for
>>> "non-blocking text-mode connections" the line is "pushed back, silently"
>>> but otherwise "accepted with a warning".
>>>
>>> My understanding is that the unz() here is blocking so the line
>>> should be accepted. Is that incorrect? If so, how would I go about
>>> reading such lines from a zip file?
>>>
>>> Best,
>>>
>>> Mikko
>>>
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