[R] Warning message about closing a connection XXXX

[Prof Brian Ripley]

On 04/01/2012 18:21, Duncan Murdoch wrote:
> On 12-01-04 12:25 PM, Prof Brian Ripley wrote:
>> On 04/01/2012 17:12, William Dunlap wrote:
>>> Re
>>> > How can I avoid the warning message altogether?
>>>
>>> ?closeAllConnections
>>>
>>> I think of calls to closeAllConnections() in the same
>>> way that I think of calls to rm(list=objects()):
>>> they both can remove things that are not theirs to remove.
>>>
>>> Calling gc() will close all unused connections, so
>>> no damage can be done. (I thought that the warning
>>> about closing unused text connections was dropped in
>>> a recent release of R so neither is really needed.)
>>
>> Yes, it was. The warning is there because the user may need to do
>> something about the 'other end' of the now-closed connection, which R
>> manages for textConnections.
>>
>> There is however one circumstance where gc() does not close all unused
>> connections, and that is when gzcon() is used (because that involves two
>> connections and it is not clear when the inner one is 'in use': and we
>> used to guess wrong).
>>
>> Rather than using a sledgehammer, use showConnections(all=TRUE) to see
>> all connections, and close the ones you want to (and its help page shows
>> you how).
>
> In older versions that do give the warning, wouldn't it be sufficient to
> name the textConnection, and close it explicitly? E.g.
>
> mydata<- read.table(con <- textConnection(mystring), header=TRUE,
> sep=",", row.names="id", na.strings=" ")
>
> close(con)

Yes, but you cannot do that retrospectively.  I would say this is still 
good practice.

> Duncan Murdoch
>
>
>>
>>> Bill Dunlap
>>> Spotfire, TIBCO Software
>>> wdunlap tibco.com
>>>
>>>> -----Original Message-----
>>>> From: r-help-bounces at r-project.org
>>>> [mailto:r-help-bounces at r-project.org] On Behalf Of David Winsemius
>>>> Sent: Wednesday, January 04, 2012 7:10 AM
>>>> To: Dan Abner
>>>> Cc: r-help at r-project.org
>>>> Subject: Re: [R] Warning message about closing a connection XXXX
>>>>
>>>>
>>>> On Jan 4, 2012, at 9:53 AM, Dan Abner wrote:
>>>>
>>>>> Hello everyone,
>>>>>
>>>>> After running the following code, I obtain this error message.
>>>>>
>>>>>
>>>>>> mydata<- read.table(textConnection(mystring),
>>>>> + header=TRUE, sep=",",
>>>>> + row.names="id", na.strings=" ")
>>>>>> mydata
>>>>> Warning message:
>>>>> closing unused connection 3 (mystring)
>>>>>
>>>>> =====
>>>>>
>>>>> However, when I attempt to run read.table() again and immediately
>>>>> submit
>>>>> the close() function (below), I obtain this message:
>>>>>
>>>>>> close(mystring)
>>>>> Error in UseMethod("close") :
>>>>> no applicable method for 'close' applied to an object of class
>>>>> "character"
>>>>> =====
>>>>>
>>>>> How can I avoid the warning message altogether?
>>>>
>>>> ?closeAllConnections
>>>>
>>>> The error message occurs because "mystring was never the connection
>>>> name.
>>>>
>>>> --
>>>>
>>>> David Winsemius, MD
>>>> West Hartford, CT
>>>>
>>>> ______________________________________________
>>>> R-help at r-project.org mailing list
>>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>>> PLEASE do read the posting guide
>>>> http://www.R-project.org/posting-guide.html
>>>> and provide commented, minimal, self-contained, reproducible code.
>>>
>>> ______________________________________________
>>> R-help at r-project.org mailing list
>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>> PLEASE do read the posting guide
>>> http://www.R-project.org/posting-guide.html
>>> and provide commented, minimal, self-contained, reproducible code.
>>
>>
>


-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595