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MathGroup Archive 1999

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Re: problem with Part function

  • To: mathgroup at smc.vnet.net
  • Subject: [mg18190] Re: [mg18172] problem with Part function
  • From: BobHanlon at aol.com
  • Date: Mon, 21 Jun 1999 22:50:33 -0400
  • Sender: owner-wri-mathgroup at wolfram.com

Dario,

Use ReplacePart

mat = Table[Table[0, {5}], {5}];
xy = {3, 3};
mat = ReplacePart[mat, 1, xy]

{{0, 0, 0, 0, 0}, {0, 0, 0, 0, 0}, {0, 0, 1, 0, 0}, {0, 0, 0, 0, 0}, {0, 0, 0,
     0, 0}}

xy2 = Table[{n, n}, {n, Length[mat]}];
mat = ReplacePart[mat, 1, xy2]

{{1, 0, 0, 0, 0}, {0, 1, 0, 0, 0}, {0, 0, 1, 0, 0}, {0, 0, 0, 1, 0}, {0, 0, 0,
     0, 1}}

val = Range[Length[mat]];
valPos = Table[{n}, {n, Length[mat]}];
mat = ReplacePart[mat, val, xy2, valPos]

{{1, 0, 0, 0, 0}, {0, 2, 0, 0, 0}, {0, 0, 3, 0, 0}, {0, 0, 0, 4, 0}, {0, 0, 0,
     0, 5}}

Bob Hanlon

In a message dated 6/20/99 2:27:38 AM, bubbola at workline.it writes:

>I've a matrix of zeros, say:
>mat=Table[Table[0,{5}],{5}];
>then, I've a point in xy axys,
>xy={3,3};
>now, I want the position {3,3} of matrix becomes 1;
>if I write
>mat[[xy]]=1; or mat[[{3,3}]]=1; it doesn't work; only mat[[3,3]]=1 
>works, but I don't want rewrite all.
>I think I've to use something like Map, Thread, Apply or so, but I don't
>
>know what and how exactely;
>


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