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MathGroup Archive 2007

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Re: Find index of maximal element in multi-dimensional

  • To: mathgroup at smc.vnet.net
  • Subject: [mg73544] Re: [mg73492] Find index of maximal element in multi-dimensional
  • From: Bob Hanlon <hanlonr at cox.net>
  • Date: Wed, 21 Feb 2007 01:54:14 -0500 (EST)
  • Reply-to: hanlonr at cox.net

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

Last[Sort[Flatten[MapIndexed[{#2, #1} & , z, {2}], 1], 
   OrderedQ[{#1[[2]], #2[[2]]}] & ]]

{{4,6},0.94111}

{Position[z,#][[1]],#}&[Max[z]]

{{4,6},0.94111}

Your approach does not work for arrays of higher dimension

z = Table[Random[], {5}, {6},{4}] ;

Last[Sort[Flatten[MapIndexed[{#2, #1} & , z, {2}], 1], 
   OrderedQ[{#1[[2]], #2[[2]]}] & ]]

{{5,5},{0.890354,0.0253132,0.877603,0.981199}}

{Position[z,#][[1]],#}&[Max[z]]

{{5,1,3},0.998183}


Bob Hanlon

---- Andrew Moylan <andrew.j.moylan 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



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