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MathGroup Archive 2004

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Re: Understanding Flatten

  • To: mathgroup at smc.vnet.net
  • Subject: [mg46324] Re: [mg46314] Understanding Flatten
  • From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
  • Date: Sat, 14 Feb 2004 04:37:59 -0500 (EST)
  • References: <200402140258.VAA08621@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

On 14 Feb 2004, at 03:58, Harold Noffke wrote:

> Mathematica 5.0.1 on Windows 2000
> MathGroup:
>
> In my study of Flatten, the Mathematica Book gives this example ...
>
> 	You can use Flatten to "splice" sequences of elements into lists
> 	or other expressions.
>
> 	In[5]:= Flatten[ {a, f[b, c], f[a, b, d]}, 1, f ]
>
> 	Out[5]= {a,b,c,a,b,d}
>
> I modified In[5] as follows ...
>
> 	In[1]:= Flatten[ { {a, f[b, c], f[a, b, d]}, {g, f[e, g]} }]
>
> 	Out[1]= {a, f[b, c], f[a, b, d], g, f[e, g]}	
> 	
> I don't see why adding {g, f[e, g]} as a second list to the In[5] 
> example
> unflattens Flatten's answer.  What am I misunderstanding?
>
> Thanks.
> Harold
>
>
The two examples are quite different. In the first you are using the 
form

Flatten[expr,1, f]

which falttens to level 1 all subexpresions (on level 1) with Head f .

In your second case you are using just

Flatten[expr].

To see both together:


Flatten[Flatten[{{a,f[b,c],f[a,b,d]},{g,f[e,g]}}],1,f]

{a,b,c,a,b,d,g,e,g}


Andrzej Kozlowski
Chiba, Japan
http://www.mimuw.edu.pl/~akoz/


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