[Rd] Canberra distance

[Christophe Genolini]

The definition I use is the on find in the book "Cluster analysis" by 
Brian Everitt, Sabine Landau and Morven Leese.
They cite, as definition paper for Canberra distance, an article of 
Lance and Williams "Computer programs for hierarchical polythetic 
classification" Computer Journal 1966.
I do not have access, but here is the link : 
http://comjnl.oxfordjournals.org/cgi/content/abstract/9/1/60
Hope this helps.

Christophe
> On 06/02/2010 10:39 AM, Christophe Genolini wrote:
>> Hi the list,
>>
>> According to what I know, the Canberra distance between X et Y is : 
>> sum[ (|x_i - y_i|) / (|x_i|+|y_i|) ] (with | | denoting the function 
>> 'absolute value')
>> In the source code of the canberra distance in the file distance.c, 
>> we find :
>>
>>     sum = fabs(x[i1] + x[i2]);
>>     diff = fabs(x[i1] - x[i2]);
>>     dev = diff/sum;
>>
>> which correspond to the formula : sum[ (|x_i - y_i|) / (|x_i+y_i|) ]
>> (note that this does not define a distance... This is correct when 
>> x_i and y_i are positive, but not when a value is negative.)
>>
>> Is it on purpose or is it a bug?
>
> It matches the documentation in ?dist, so it's not just a coding 
> error.  It will give the same value as your definition if the two 
> items have the same sign (not only both positive), but different 
> values if the signs differ.
>
> The first three links I found searching Google Scholar for "Canberra 
> distance" all define it only for non-negative data.  One of them gave 
> exactly the R formula (even though the absolute value in the 
> denominator is redundant), the others just put x_i + y_i in the 
> denominator.
>
> None of the 3 papers cited the origin of the definition, so I can't 
> tell you who is wrong.
>
> Duncan Murdoch
>
>