Message-ID: <k4l870p6eqfisbutc4e5a6a0it2gebufeu@4ax.com>
Date: 2004-04-07T21:38:52Z
From: Duncan Murdoch
Subject: More user-friendly error message needed.
In-Reply-To: <1081364866.2239.4.camel@dhcp9931.dhcp.unc.edu>
(Moved from r-help to r-devel).
On 07 Apr 2004 15:07:49 -0400, Shin <sdhyok@email.unc.edu> wrote :
>When I tried the following commands, I got a strange message.
>
>
>> x<-data.frame(y=c(1:10))
>> plot(x$z)
>Error in xy.coords(x, y, xlabel, ylabel, log) :
> x and y lengths differ
>
>"The data frame, x, does not have a field named z."
>may be better user-friendly message for this kind of common error.
There are several places this could be fixed. When you use x$z, the
code for $ could give an error message or a warning; instead it
returns NULL with no error or warning. Changing this would probably
be dangerous: I'd guess there's code out there that relies on getting
a NULL back from a construction like that. But maybe we should change
that in 2.0?
Then plot(NULL) is called, which eventually results in the message you
saw. That could be easily fixed: plot.default could have
if (is.null(x)) stop("x is NULL")
I can't think of a reason why this would cause trouble. However, if
you had something like
plot(x$y, x$z)
the error wouldn't be detected.
Finally, the actual error message comes from a bug in the xy.coords
code: it has
y <- x
x <- 1:length(x)
for the case where there is a NULL y supplied, and this is wrong: it
should be x <- seq(along=x). Making just this fix gives a fairly
inscrutable error message:
Error in plot.window(xlim, ylim, log, asp, ...) :
need finite xlim values
In addition: Warning messages:
1: no finite arguments to min; returning Inf
2: no finite arguments to max; returning -Inf
3: no finite arguments to min; returning Inf
4: no finite arguments to max; returning -Inf
but this might be easier to figure out than the original one.
Duncan Murdoch