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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: [mg77361] Re: apparently I don't know how to use Map (or Apply or MapThread)
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Thu, 7 Jun 2007 03:53:34 -0400 (EDT)
  • Organization: Uni Leipzig
  • References: <f4676i$1n3$1@smc.vnet.net>
  • Reply-to: kuska at informatik.uni-leipzig.de

Hi,

you mean

Table[#[[i, i]], {i, Length[#]}] &@ m

or with (Mathematica 6.0)*

Diagonal[m]

or if you whant to use Map*[]

Reap[MapIndexed[If[Equal @@ #2, Sow[#1]] &, m, {2}]][[2, 1]]

or

First /@ MapIndexed[RotateLeft[#1, #2[[1]] - 1] &, m]

or

MapIndexed[ #1[[#2[[1]]]] &, m]

or
MapIndexed[ First @ Take[#1, #2] &, m]

Regards
   Jens

dbsearch04 at yahoo.com wrote:
> 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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