arr.ind argument to which.min and which.max
For what it's worth, see arrayIndex() in R.utils, e.g. # Single index print(arrayIndex(21, dim=c(4,3,3))) # Multiple indices print(arrayIndex(20:23, dim=c(4,3,3))) # Whole array x <- array(1:30, dim=c(5,6)) print(arrayIndex(1:length(x), dim=dim(x))) # Find (row,column) of maximum value m <- diag(4-abs(-4:4)) print(arrayIndex(which.max(m), dim=dim(m))) /Henrik
On Mon, Jul 5, 2010 at 8:27 PM, Patrick Burns <pburns at pburns.seanet.com> wrote:
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'. Pat
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 http://www.burns-stat.com (home of 'Some hints for the R beginner' and 'The R Inferno')
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