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MathGroup Archive 2007

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Re: apparently I don't know how to use Map (or Apply or MapThread)

  • To: mathgroup at smc.vnet.net
  • Subject: [mg77401] Re: apparently I don't know how to use Map (or Apply or MapThread)
  • From: "Drago Ganic" <dganic at vodatel.net>
  • Date: Thu, 7 Jun 2007 04:14:29 -0400 (EDT)
  • Organization: Customer of Vodatel, Zagreb, CROATIA
  • References: <f4676i$1n3$1@smc.vnet.net>

Hi,
here is a "neat" example which uses Pick:
Flatten[Pick[m, Array[Equal, Dimensions[m]]]]
{0.098, 0.914}


This construct uses MapIndexed:
Reap[MapIndexed[ Sow[#1,  SameQ @@ #2 ] &, m , {2} ]; , True] [[2, 1]]
{0.098, 0.914}

Greetings from Croatia,
Drago

<dbsearch04 at yahoo.com> wrote in message news:f4676i$1n3$1 at smc.vnet.net...
>I started with this:
>
> m = {{0.098, 0.951, 0.954}, {0.509, 0.914, 0.487}}
>
> I tried to do this
>
> Table[#[[i, i]], {i, Length[#]}] & /@ m
>
> It does not work, but this works
>
> Diag := Function[x, Table[x[[i, i]], {i, Length[x]}]]; Diag[m]
>
> !@#$%^&*(
>
> Can anyone tell me why? I also tried: Apply, MapThread,
> DiagonalMatrix, TakeMatrix, adding () around the pure function...
>
> I know that this is a simple problem. Would Evaluate help?
>
> TIA.
>
> Regards..
>
> 




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