[R] fun.aggregate=mean in reshape

[Peter Dalgaard]

Charilaos Skiadas wrote:
> On Feb 12, 2008, at 1:31 PM, [Ricardo Rodriguez] Your XEN ICT Team  
> wrote:
>
>   
>> Sundar Dorai-Raj wrote:
>>
>> Could it we advisable that cast, melt or whatever function we deal  
>> with
>> throws an more informative error message when this kind of conflicts
>> occur? I am guessing this is a pretty frequent situation, so if it is
>> not done there must be a number of good reasons!
>>
>> Just my two cents!
>>
>>     
>
> I think this is appropriate here:
>
>  > library(fortunes)
>  > fortune("dog")
>
> Firstly, don't call your matrix 'matrix'. Would you call your dog  
> 'dog'? Anyway, it might clash
> with the function 'matrix'.
>     -- Barry Rowlingson
>        R-help (October 2004)
>
>
> in other words, it is advisable that you don't call anything "mean".  
> The error seems to be almost as clear as it could in this case:
>
> Error in get(as.character(FUN), mode = "function", envir = envir) :
>    variable "fun" of mode "function" was not found
>
> It tells you that a call to get was attempted looking for a variable  
> of mode "function", and such a variable was not found. The problem is  
> of course that the call tells you the variable is named "fun", while  
> you expected it to be named "mean". But it alerts to the fact that  
> the program was expecting a function in a place where it was given  
> something else, and there is only one place where you provide it a  
> function.
>   
This does however sound like the author missed the opportunity to use 
match.fun() (see, e.g. how it is used inside lapply()). This is exactly 
designed to avoid picking up non-function objects. I haven't actually 
read the code, though, so there could be reasons.

> Also, the fact that the call works fine without the fun.aggregate, or  
> with a different fun.aggregate, prompts to the problem being the word  
> "mean".
> Then typing "mean" followed by return would show you, instead of the  
> function body for  the function mean, something quite different.
> I have to admit that a cursory look at the code for cast does not  
> immediately tell me where "fun" shows up, however, so I am slightly  
> mystified by the error.
>
>   
>> Thanks for your help,
>>
>> Ricardo
>>
>> -- 
>> Ricardo Rodríguez
>> Your XEN ICT Team
>>     
>
> Haris Skiadas
> Department of Mathematics and Computer Science
> Hanover College
>
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>   


-- 
   O__  ---- Peter Dalgaard             Øster Farimagsgade 5, Entr.B
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