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MathGroup Archive 2004

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RE: Padding arrays with reversed elements

  • To: mathgroup at smc.vnet.net
  • Subject: [mg45685] RE: [mg45636] Padding arrays with reversed elements
  • From: "Wolf, Hartmut" <Hartmut.Wolf at t-systems.com>
  • Date: Mon, 19 Jan 2004 05:15:30 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

>-----Original Message-----
>From: Mariusz Jankowski [mailto:mjankowski at usm.maine.edu]
To: mathgroup at smc.vnet.net
>Sent: Saturday, January 17, 2004 1:57 AM
>To: mathgroup at smc.vnet.net
>Subject: [mg45685] [mg45636] Padding arrays with reversed elements
>
>
>Hi all, a recently posted question on "creating a toroidal 
>data structure"
>and the the responses have inspired me to post the following 
>similar but
>harder problem. I am interested in "reflected" padding of 
>multidimensional
>arrays. Here is an example in 1D:
>
>{a,b,c,d} -> {a,b,c,d,d,c,b,a,a,b,c,d,d,c, etc}
>
>also the padding should be possible on the left or right or both and of
>course, the length is an argument. I have a complicated 
>looking solution
>using PadRight, Fold, Partition and would love to see some 
>ideas leading to
>a possibly simpler solution.
>
>Thanks, Mariusz
>


Mariuz,

PadRight still going strong:

In[1]:= r = {a, b, c, d};

In[2]:= rr = Join[r, Reverse[r]]
Out[2]= {a, b, c, d, d, c, b, a}

In[3]:= PadRight[rr, 14, rr]
Out[3]=
{a, b, c, d, d, c, b, a, a, b, c, d, d, c}

In[4]:= PadRight[rr, 8, rr, 2]
Out[4]= 
{b, a, a, b, c, d, d, c}

--
Hartmut Wolf


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