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MathGroup Archive 2007

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Re: sparsearray and its nonempty cells

  • To: mathgroup at smc.vnet.net
  • Subject: [mg72607] Re: sparsearray and its nonempty cells
  • From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
  • Date: Fri, 12 Jan 2007 05:13:36 -0500 (EST)
  • Organization: The Open University, Milton Keynes, UK
  • References: <eo4oa3$mhi$1@smc.vnet.net>

Arkadiusz.Majka at gmail.com wrote:
> Hi,
> 
> I bulit the following sparse array
> 
> Mysparse=SparseArray[i_ /; 2 â?¤ i â?¤ 11 :> 0.8, 20]
> 
> in order to find out all nonempty cells in this array I call (I want to
> avoid Normal)
> 
> 
> Mysparse/. SparseArray[_, _, _, x_] :> x[[2, 2]]
> 
> and I get
> 
> {{8}, {11}, {3}, {7}, {2}, {6}, {10}, {9}, {5}, {4}}
> 
> This is of course correct, but why it is not sorted????
> 
> How can I build Mysparse to get sorted list of nonempty cells?
> 
> Arek

Hi Arek,

What about the following:

In[1]:=
Mysparse = SparseArray[i_ /; 2 <= i <= 11 :> 0.8, 20];
Sort[Mysparse /. SparseArray[_, _, _, x_] :> x[[2,2]]]

Out[2]=
{{2}, {3}, {4}, {5}, {6}, {7}, {8}, {9}, {10}, {11}}

HTH,
Jean-Marc


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