On Tue, 26 Aug 2008, Eric DeWitt wrote:
I encountered an error that does not make sense to me given my reading
of the documentation and does not appear to be referenced in the list
archives or online. The error occurred when a function received a NULL
value rather than a numeric value as a parameter and then attempted to
use the NULL value in the calculateion. The error: "Error during wrapup:
nothing to replace with" can be easily recreated with the following code:
1 + NULL # note that the opperation succeeds and returns a numeric vector with
dim(NULL)
numeric(0)
As documented, of course.
bar <- 1
bar
[1] 1
foo <- 1 + NULL
foo
numeric(0)
bar <- bar + foo # note that here the assignment operation succeeds and 1 + (1 +
NULL) -> numeric(0)
bar
numeric(0)
bar <- c(1, 1) # however if the assignment is into a vector
bar[1] <- bar[1] + foo # note that the mathematical operation is identical, but
the assignment fails
Error during wrapup: nothing to replace with
That's the trouble, this is not the same operation at all. This is
replacing one element of a vector, not naming the result 'bar'.
If this is the intended behavior, a more informative error message (e.g.
'attempt to assign NULL to vector element') would be useful. If it is
not the intended behavior, should I log this as a bug?
It is the intended and documented behaviour. You tried to set element 1 of
bar to bar[1] + foo, which is numeric(0) (by the documented recycling
rules). The error message: 'nothing to replace with' seems very
informative to me. If you put some effort into understanding your own
errors by doing things step by step, as in
bar <- c(1, 1)
foo <- bar[1] + foo
bar[1] <- foo
Error in bar[1] <- foo : nothing to replace with
foo
numeric(0)
you might learn more.
I don't know how you got an 'Error during wrapup': that is not
reproducible (it might be a function of using a console, if you did).
-eric
sessionInfo()
R version 2.7.1 (2008-06-23)
powerpc-apple-darwin8.10.1
locale:
en_US.UTF-8/en_US.UTF-8/C/C/en_US.UTF-8/en_US.UTF-8
attached base packages:
[1] stats graphics grDevices utils datasets methods base
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--
Brian D. Ripley, [EMAIL PROTECTED]
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)
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