On Fri, Jan 3, 2013, Bert Gunter wrote
Well...
On Thu, Jan 3, 2013 at 10:00 AM, ivo welch <ivo.welch <at>
anderson.ucla.edu> wrote:
Dear R developers---I just spent half a day debugging an R program,
which had two bugs---I selected the wrongly named variable, which
turns out to have been a scalar, which then happily multiplied as if
it was a matrix; and another wrongly named variable from a data
frame,
that triggered no error when used as a[["name"]] or a$name . there
should be an option to turn on that throws an error inside R when
one
does this. I cannot imagine that there is much code that wants to
reference non-existing columns in data frames.
But I can -- and do it all the time: To add a new variable, "d" to a
data frame, df, containing only "a" and "b" (with 10 rows, say):
df[["d"]] <- 1:10
Yes but that's `[[<-`. Ivo was talking about `[[` and `$`; i.e., select
only not assign, if I understood correctly.
Trying to outguess documentation to create error triggers is a very
bad idea.
Why exactly is it a very bad idea? (I don't necessarily disagree, just
asking
for more colour.)
R already has plenty of debugging tools -- and there is even a "debug"
package. Perhaps you need a better programming editor/IDE. There are
several listed on CRAN, RStudio, etc.
True, but that relies on you knowing there's a bug to hunt for. What if
you
don't know you're getting incorrect results, silently? In a similar way
that options(warn=2) turns known warnings into errors, to enable you to
be
more strict if you wish, an option to turn on warnings from `[[` and
`$`
if the column is missing (select only, not assign) doesn't seem like a
bad option to have. Maybe it would reveal some previously silent bugs.
Anyway, I'm hoping Ivo will let us know if he likes the simple mask I
proposed, or not. That's already an option that can be turned on or
off.
But if his bug was selecting the wrong column, not a missing one, then
I'm not sure anything could (or needs to be) done about that.
Matthew
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