[R] Error with function lda in package MASS (dimnames not equal?)

[Prof Brian Ripley]

The code will be changed to give a more informative error message in a 
future release.  However, do remember that this is volunteer code, and it 
is not reasonable to expect volunteers to anticipate that a user will 
apply it in extremely unlikely circumstances.

If you have a suggestion about code in a contributed package, please send 
it to the package maintainer (as the posting guide asks).

On Sat, 11 Jun 2005, Joshua Gilbert wrote:

> This is true, they are equal. I hadn't noticed that. Thank you.
>
> Now, if lda fails on this given input (equal means), shouldn't we
> catch it and give a slightly better error message? I've spent a good
> while going through the debugging process with lda.default. From that
> perspective it appears that there is a simple change to remove the
> problem. I am not saying that it is correct in any shape or form, but
> there is a point where a single transpose would silence the error.
>
> So, from a usability standpoint, could we add a check for equal means
> between classes and throw an error for that specific condition? Yes,
> the user should not do that. But users may become more interested in
> making the code run than checking on whether it's doing anything sane.
>
> If this isn't the place to do so, tell me. But, I'd like to petition
> to alter the code of lda.default.
>
> On 6/10/05, Prof Brian Ripley <ripley at stats.ox.ac.uk> wrote:
>> lda.default <- MASS:::lda.default and proceed.
>>
>> Look at the group means of your data: they are identical to machine
>> accuracy.
>>
>> The question has to be `why are you trying to use lda to separate
>> two groups with identical means'?  Lda is not protected against that
>> and it is rather unlikely unless you failed to inspect your data in any
>> way.
>>
>> On Fri, 10 Jun 2005, Joshua Gilbert wrote:
>>
>>> This question appears to have been asked previously, but not answered.
>>> the last response I can find to this previous thread is here:
>>> http://tolstoy.newcastle.edu.au/R/help/04/07/0126.html. The asnwer was
>>> to provide debugging info, not an answer.
>>>
>>> So the problem is that I'm trying to use lda on my dataset. You can
>>> download my data here:
>>> http://northstar-www.dartmouth.edu/~jgilbert/nolda, I used R's save
>>> function to save objects data and classes (yes, I realize that I name
>>> stomped the data function in package utils). To replicate my results,
>>> simply enter the following:
>>>> library(MASS)
>>>> load('nolda')
>>>> lda(data,classes)
>>> Error in lda.default(x, grouping, ...) : length of 'dimnames' [2] not
>>> equal to array extent
>>>
>>> Now, I don't know what that means.
>>>> dimnames(data)
>>> NULL
>>>> dimnames(classes)
>>> NULL
>>>
>>> As for debugging, I don't know how. I cannot debug lda.default as I
>>> get the following:
>>>> debug(lda.default)
>>> Error: Object "lda.default" not found
>>>
>>> I think that that's pretty much it. Can anyone help me?
>>>
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>>>
>>
>> --
>> 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
>>
>
>

-- 
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