Re: unexpected failure on all formulas

[Christian Moe <mail@christianmoe.com>]

Hi, Nick,

No whacks intended! It was an easy catch because I was mulling over 
similar problems with my code. My own second pass at a vmode 
implementation for Calc is below, now with support for negative values 
and bimodal data. It takes a different route and is a bit shorter, but 
doesn't handle all the cases your code does (I guess; I don't grok it 
all).

Yours,
Christian


(defmath vmode (vec)
   "Return the mode(s), i.e. most frequent value(s), of a vector
   of integers VEC."
   (let ((results (vec)) ; hold results
         (index 1)
         offset maxfreq)
     (setq offset (- 1 (vmin vec))
           vec (+ offset vec) ; bump all ints positive
           freq (histogram vec (1+ (vmax vec)))
           offset (1+ offset) ; histogram added `0' slot
           maxfreq (vmax freq))
     ;; Collect indexes (less offset) of all max freqs
     (while (> (setq index (find freq maxfreq index)) 0)
       (setq results (vconcat results index)
             index (1+ index)))
     (setq results (- results offset)) ; get neg ints back
     ;; Return results as vector or number
     (if (> (vlen results) 1)
         results
       (head results))))


On 9/20/11 4:59 PM, Nick Dokos wrote:
> Christian Moe<mail@christianmoe.com>  wrote:
>
>
>> I think your vmode() needs to subtract one from the result. The mode
>> in the "systolic" column of Jude's dataset should be 124 (f=12), not
>> 125 (f=2).
>>
>
> Yes, this is an off-by-one error: in vfreqs, I should cons prev onto
> freqs, not (nth 0 vec). In addition to this and the multimodal problem
> that both you and Lawrence Mitchell pointed out, there is another
> off-by-one error when vfreqs gets to the end of the list.
>
> All in all, a disaster: can a posting be deleted? or at least marked
> with a big, red X so that it won't mislead in the future? I'll try to
> post a corrected version later on.
>
> OTOH, my main interest in this was the hooking up of a user function
> onto calc and the example, though deeply flawed, does illustrate that.
>
> Thanks to both Christian and Lawrence for the whacks in the head
> (although now I have a headache...)
>
> Nick