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MathGroup Archive 2005

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Re: "expanding a list"

  • To: mathgroup at smc.vnet.net
  • Subject: [mg57940] Re: [mg57860] "expanding a list"
  • From: Ken Levasseur <klevasseur at mac.com>
  • Date: Mon, 13 Jun 2005 05:51:01 -0400 (EDT)
  • References: <200506100629.CAA15653@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

My first reaction was to use a pattern and rule.

In[56]:=
expandlistRule[j_, k_] :=
   {{a_, b___} :> Join[{Table[a, {j}]},
      (Table[#1, {k}] & ) /@ {b}]}

In[57]:=
Range[5] /. expandlistRule[4, 2]

Out[57]=
{{1, 1, 1, 1}, {2, 2}, {3, 3}, {4, 4}, {5, 5}}

In[58]:=
Range[1] /. expandlistRule[4, 2]

Out[58]=
{{1, 1, 1, 1}}

In[59]:=
Range[5] /. expandlistRule[0, 2]

Out[59]=
{{}, {2, 2}, {3, 3}, {4, 4}, {5, 5}}

In[61]:=
Range[5] /. expandlistRule[2, 0]

Out[61]=
{{1, 1}, {}, {}, {}, {}}


On Jun 10, 2005, at 2:29 AM, Mark Coleman wrote:

> Greetings,
>
> I'd like to construct a list as follows. Say I have a list of reals
> {x1,x2,x3,...xn}, and another list of integers {r,s}. I'd like to
> make a new list
>
> {{x1,x1,x1,...},{x2,x2,x2....},{x3,x3,x3,...},....,{xn,xn,xn,...}},
> where the first sublist is of length r, and the remaining sublists
> are of length s.
>
>
> Thanks,
>
> -Mark
>
>
>
>

Ken Levasseur
http://homepage.mac.com/klevasseur/


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