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MathGroup Archive 2006

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Re: bug in Partition?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg65706] Re: [mg65679] bug in Partition?
  • From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
  • Date: Sun, 16 Apr 2006 01:45:13 -0400 (EDT)
  • References: <200604140832.EAA22075@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

On 14 Apr 2006, at 17:32, Chris Chiasson wrote:

> Partition[Range[11], 3, 3, {1, 1}, Hold[]]
>
> the output is
>
> {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}, {10, 11}}
>
> I would expect
>
> {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}, {10, 11, Hold[]}}
>
> Might this be because of a ReleaseHold somewhere in the implementation
> of Partition?
>
> (Ver 5.2, Windows)
>

You are right that ReleaseHold is applied as you can see by looking  
at Trace (and noting that ReleaseHold[Hold[]] is Sequence[]) or just  
by inserting Hold[1] instead of Hold[]. But why do you think this is  
a bug? It actually gives you one more way of using Partition -  
padding with Hold[] is equivalent to using Sequence[] in the  
sublists.However,  if you try use Sequence[] directly as the last  
argument to Partition it will vanish too soon and the result will be  
the same as if you had no last argument at all.
I can't speak for WRI but I would  tend to consider this as an  
"undocumented feature". There seem to be still quite a lot of this  
kind in Mathematica;-)

Andrzej Kozlowski


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