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MathGroup Archive 2004

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[Bug] Transpose is broken for empty SparseArrays

  • To: mathgroup at smc.vnet.net
  • Subject: [mg49576] [Bug] Transpose is broken for empty SparseArrays
  • From: Scott Morrison <scott at math.berkeley.edu>
  • Date: Fri, 23 Jul 2004 06:01:48 -0400 (EDT)
  • Reply-to: scott at math.berkeley.edu
  • Sender: owner-wri-mathgroup at wolfram.com

I'm running $Version == 5.0 for Microsoft Windows (November 18, 2003)

It seems there's a bug in Transpose, when acting on an empty 
SparseArray. For example, I find that

Dimensions[Transpose[SparseArray[{},{1,2}]]]

returns {1,2}, rather than {2,1}.

For now, I'm using the following as a work-around:

If[$VersionNumber\[GreaterEqual]5\[And]
     Dimensions[Transpose[SparseArray[{},{2,1}]]]\[Equal]{2,1},
   Print["Fixing bug in Transpose"];
   Unprotect[Transpose];
   Transpose[
         m_SparseArray]/;(Length[ArrayRules[m]]\[Equal]1\[And]
           ArrayDepth[m]\[GreaterEqual]2):=Module[{dim=Dimensions[m]},
       SparseArray[{},{dim\[LeftDoubleBracket]2\[RightDoubleBracket],
         dim\[LeftDoubleBracket]1\[RightDoubleBracket]}~Join~Drop[dim,2]]
       ];
   Protect[Transpose];
   ]

but hopefully someone from Wolfram will see this and let us know about a 
more permanent solution on it's way? :-) This bug caused some hard to 
track down problems while migrating a large program from 4.2 to 5.0, so 
I'm posting it here as a 'heads-up' for everyone else.

Scott Morrison


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