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MathGroup Archive 2007

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Re: sort and positon matrix element help

  • To: mathgroup at smc.vnet.net
  • Subject: [mg73077] Re: [mg73050] sort and positon matrix element help
  • From: Sseziwa Mukasa <mukasa at jeol.com>
  • Date: Thu, 1 Feb 2007 03:39:22 -0500 (EST)
  • References: <200701310512.AAA15216@smc.vnet.net>

On Jan 31, 2007, at 12:12 AM, comp.soft-sys.math.mathematica wrote:

> Hi, guys,
>
>         I am attacking one proble and may need your help.
>         I have a large matrix(m*n). I wanna to sort out the matrix
> from large to small according to its element's value AND save the
> corresponding row and column number as its position. Latter on, plot
> out the first 20 largest value accroding to their positions.
>         Is there any good way to do this, especially take out the
> positons of element and assocate it with the value?

You can get the largest 20 elements of the array with Ordering[Flatten 
[array],-20].

Position[array,Union[Ordering[Flatten[array],-20]] will get you the  
positions of those elements including possible duplicates.

If your array is large but you only care about 20 elements, you can  
cut down your storage requirements by not storing the sorted array or  
appending position information for all the elements.

Regards,

Ssezi


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