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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: [mg73524] Re: Find index of maximal element in multi-dimensional array
  • From: "Ray Koopman" <koopman at sfu.ca>
  • Date: Wed, 21 Feb 2007 01:43:25 -0500 (EST)
  • References: <erelbt$7h4$1@smc.vnet.net>

On Feb 20, 3:17 am, "Andrew Moylan" <andrew.j.moy... at gmail.com> 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

z = Table[Random[],{5},{n = 6}]

{{0.247831, 0.85266, 0.87098,  0.840725, 0.808299, 0.160707},
 {0.692361, 0.613514,0.758175, 0.823928, 0.0331389,0.330202},
 {0.155955, 0.89171, 0.770831, 0.327228, 0.974979, 0.25434},
 {0.325965, 0.5732,  0.388035, 0.0842301,0.089699, 0.99669},
 {0.140205, 0.23157, 0.218719, 0.155965, 0.331906, 0.0708631}}

{Ceiling[#/n],Mod[#,n,1]}&@@Ordering[Flatten@z,-1]

{4,6}



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