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

Patrick Burns pburns at pburns.seanet.com
Mon Jul 5 20:27:20 CEST 2010

On 05/07/2010 10:56, Martin Maechler wrote:
>>>>>> "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 ...}

I think the exercise is just to copy the definition of
'which' and add four characters.

If the order of the if condition were reversed, then
possibly the slight reduction in speed of 'which.min'
and 'which.max' would be more than made up for in the
slight increase in speed of 'which'.


> 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')

Patrick Burns
pburns at pburns.seanet.com
(home of 'Some hints for the R beginner'
and 'The R Inferno')

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