Re: [Rd] arr.ind argument to which.min and which.max

From: Vincent Goulet <Vincent.Goulet_at_act.ulaval.ca>
Date: Tue, 06 Jul 2010 14:32:05 -0400

Le lun. 5 juil. à 05:56, Martin Maechler a écrit :

>>>>>> "PatB" == Patrick Burns <pburns_at_pburns.seanet.com>
>>>>>>    on Sun, 04 Jul 2010 09:43:44 +0100 writes:

>
> PatB> Is there a reason that 'which.min' and
> PatB> 'which.max' don't have an 'arr.ind'
> PatB> argument?
>
> well, help(which.min) tells you that they really were aimed at
> doing their job *fast* for vectors.
>
> Of course you are right and a generalization to arrays might be
> convenient at times.
>
> PatB> The context in which I wanted that was
> PatB> a grid search optimization, which seems
> PatB> like it would be reasonably common to me.
>
> well, as the author of these two functions, I can only say
>
> "patches are welcome!"
>
> and I think should be pretty simple, right ?
> You just have to do very simple remapping of the 1d index 'i' back
> to the array index, i.e., the same operation
> you need to transform seconds into days:hours:minutes:seconds
> {{and yes, we old-timers may recall that APL had an operator (I
> think "T-bar") to do that ...}

Ah, a reference to APL! That made my day. :-)

APL was very big among actuaries for a long time. I heard recently that it was still in use on an old system in some small insurance company. I still have on my shelves the reference books for APL*Plus III for Windows (that I ran in OS/2) from Magnugistics; they have an actuarial formula on the cover.

I teach my students arbitrary base conversion to do just what the encode/decode operators (to call them by their names) were doing. I see this new arrayInd() sort of does the same thing now. Darn, this steals me an exercise!

Cheers,

Vincent

>
> Martin Maechler, ETH Zurich
>
>
> PatB> --
> PatB> Patrick Burns
> PatB> pburns_at_pburns.seanet.com
> PatB> http://www.burns-stat.com
> PatB> (home of 'Some hints for the R beginner'
> PatB> and 'The R Inferno')
>
> ______________________________________________
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