[Rd] Bug in Sweave? -- scoping problem? (PR#8615)

murdoch@stats.uwo.ca murdoch at stats.uwo.ca
Sun Feb 19 14:41:18 CET 2006

Berwin A Turlach wrote:
> G'day Duncan,
>>>>>>"DM" == murdoch  <murdoch at stats.uwo.ca> writes:
>     DM> I have found a strange scoping problem in Sweave.  [...]
>     DM> The strange thing is that while the value in partytotal is
>     DM> output correctly as [...]
>     DM> but the dotchart contains the wrong values: it shows sorted
>     DM> values, but not sorted names, [...]
> No bug, but a feature. :)
> (But then, a well known software producer seems to use `feature' as a
> euphemism for `bug', so perhaps I shouldn't call it a feature.)
> There was recently a discussion on r-help (?) about Sweave producing
> different output in the text and plot when random numbers were
> generated, and it seems as if you have run into the same trap:
>       Code in chunks that produce pictures is executed several times.
>       First, to produce the output in the text.  And then once more
>       for *each* format in which the figure has to be produced.  I.e.,
>       if you want a PDF and a PostScript version of the figure, the
>       code is executed a total of three times.

Thanks, that's what caught me.  Is that a quote from the discussion, or 
from the docs somewhere?  It makes sense in hindsight, but it's not 
obvious ahead of time, so it should be stated fairly prominently in the 

Duncan Murdoch
> All instances of this feature reported so far involved commands that
> produced random numbers and the poster was surprised that the output
> in the text and the figures differed (and that the two figures were
> different).
> In your case the first execution of the code assigns the names to
> partytotal, sorts partytotal and produces the data.  On the next
> execution, when the picture is produced, partytotal is already sorted
> but you reassign the names.  Then the partytotal is sorted again and
> the plot is produced.  But that re-assigning of names lead to the
> disconnect between values and names.
> Hope this helps.
> Cheers,
>         Berwin
> ========================== Full address ============================
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