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MathGroup Archive 2001

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Re: Greatest element in list

  • To: mathgroup at smc.vnet.net
  • Subject: [mg30491] Re: Greatest element in list
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Fri, 24 Aug 2001 04:05:51 -0400 (EDT)
  • Organization: Universitaet Leipzig
  • References: <9m27in$gqd$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,

without your data I can't reproduce the problem.
But

MaxPosition = Compile[{{lst, _Real, 1}}, Module[{max = First[lst], pos =
1, i = 2},
      Scan[
        If[# > max, max = #; pos = i++, i++] & ,
        Rest[lst]
        ];
      pos
      ]
    ]

is atleast faster than Position[#, Max[#]] &[lst]

In[]:=lst = Table[Random[], {1000000}];

In[]:=Timing[Position[#, Max[#]] &[lst]]
Out[]={6.85 Second, {{602020}}}

In[]:=Timing[MaxPosition[lst]]
Out[]={4.42 Second, 602020}

Because it scans the list only once.

Regards
  Jens


Oliver Friedrich wrote:
> 
> Hi,
> 
> what's the best way to get the position of the greatest number in list of
> reals? I've tried
> 
> Position[#,Max[#]]&list
> 
> but surprisingly, it doesn't work all the time, sometimes it returns an
> empty list. How is that, because a theorem says that a non empty set of real
> numbers must have at least one biggest element. So Max[#] can't be empty.
> 
> Any solutions ?
> 
> Oliver Friedrich


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