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MathGroup Archive 2007

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Re: Find index of maximal element in multi-dimensional array

  • To: mathgroup at smc.vnet.net
  • Subject: [mg73548] Re: Find index of maximal element in multi-dimensional array
  • From: Oliver Ruebenkoenig <ruebenko at uni-freiburg.de>
  • Date: Wed, 21 Feb 2007 01:56:27 -0500 (EST)
  • References: <erelbt$7h4$1@smc.vnet.net>

Hi,

how about

n1 = n2 = 1000;
z = Table[Random[], {n1}, {n2}];
f2 = Compile[ {{z, _Real, 2 }}, Position[z, Max[z] ] ];
(res = f2[z]) // Timing
z[[ Sequence @@ res[[1]] ]] - Max[z]

Oliver

On Tue, 20 Feb 2007, Andrew Moylan wrote:

> Hi all,
>
> Here's a two-dimensional array of numbers:
>
> z = Table[Random[], {5}, {6}]
>
> What's an efficient way of finding the index of the maximal element of
> z? Here's one way:
>
> Last[Sort[Flatten[MapIndexed[{#2, #1} & , z, {2}], 1],
>   OrderedQ[{#1[[2]], #2[[2]]}] & ]]
>
> The output is like this:
>
> {{5, 4}, 0.921344}
>
> But it's so untidy. Any better ideas?
>
> Cheers,
>
> Andrew
>
>
>

Oliver Ruebenkoenig, <ruebenko AT uni-freiburg.de>


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