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MathGroup Archive 1996

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Re: Programming: Replace Heads

  • To: mathgroup at smc.vnet.net
  • Subject: [mg5213] Re: [mg5161] Programming: Replace Heads
  • From: yokoi at skk.is.tohoku.ac.jp (Yokoi Takahisa)
  • Date: Fri, 15 Nov 1996 03:22:34 -0500
  • Sender: owner-wri-mathgroup at wolfram.com

My solution is 
% //. (head:_) [args___] :> List[args] /; (List =!= head)

See below:
========================================================
In[188]:=
Clear[a,b,c,d,e,f,g]
f := ({a,b,c,d,e,g}[[Random[Integer, {1,6}] ]])
Array[ Hold at f, {3,2,3},1, Hold at f]//ReleaseHold

% //. (head:_) [args___] :> List[args] /; (List =!= head)

Out[190]=
d[c[a[b[1, 1, 1], e[1, 1, 2], e[1, 1, 3]], 
   b[a[1, 2, 1], e[1, 2, 2], a[1, 2, 3]]], 
  e[b[e[2, 1, 1], g[2, 1, 2], g[2, 1, 3]], 
   e[b[2, 2, 1], g[2, 2, 2], e[2, 2, 3]]], 
  c[e[g[3, 1, 1], e[3, 1, 2], c[3, 1, 3]], 
   g[e[3, 2, 1], a[3, 2, 2], a[3, 2, 3]]]]

Out[191]=
{{{{1, 1, 1}, {1, 1, 2}, {1, 1, 3}}, 
   {{1, 2, 1}, {1, 2, 2}, {1, 2, 3}}}, 
  {{{2, 1, 1}, {2, 1, 2}, {2, 1, 3}}, 
   {{2, 2, 1}, {2, 2, 2}, {2, 2, 3}}}, 
  {{{3, 1, 1}, {3, 1, 2}, {3, 1, 3}}, 
   {{3, 2, 1}, {3, 2, 2}, {3, 2, 3}}}}
========================================================

At  1:34 96/11/06 -0500, Xah Lee wrote:
Lee>Problem:
Lee>Given an abritrary expression, how to replace all heads to List?
Lee>
Lee>my solution:
Lee>Map[ {(Sequence@@#)}&, expr, {0,-2}]
Lee>
Lee>Example:
Lee>Clear[a,b,c,d,e,f,g]
Lee>f := ({a,b,c,d,e,g}[[Random[Integer, {1,6}] ]])
Lee>Array[ Hold at f, {3,2,3},1, Hold at f]//ReleaseHold
Lee>Map[ {(Sequence@@#)}&, %, {0,-2}]

*  Yokoi Takahisa <yokoi at skk.is.tohoku.ac.jp>
**  Graduate School of Information Science,
***  Tohoku Univ. <Tonpei>, Sendai, Japan



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