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MathGroup Archive 2004

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Re: i don't understand mapping function over a long list

  • To: mathgroup at smc.vnet.net
  • Subject: [mg47819] Re: i don't understand mapping function over a long list
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Thu, 29 Apr 2004 00:33:36 -0400 (EDT)
  • Organization: Universitaet Leipzig
  • References: <c6l7v9$iq0$1@smc.vnet.net>
  • Reply-to: kuska at informatik.uni-leipzig.de
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,

a) you can't get {{x$299, x$300, x$301} + 2,..}
   because Mathematica will distribute the scalar 
   addition over the lists an you will always end
   with {{x$299+2, x$300+2, x$301+2},..}
b) you can use an new symbol that is not a List with

   l = vector @@@ Partition[Flatten[{Table[Unique[x], {n, 1, 30}]}], 3];

   and
   l+2 

c) you can assign the result to

   unames = Table[Unique[u], {10}];

   with
   
   Set @@@ Transpose[{unames, (l + 2)}]

Regards
  Jens

will produce the desired result.
  
sean kim wrote:
> 
> hello group.
> 
> i just don't get this.
> 
> I'm not sure what's the problem is.
> 
> please consider the following list of lists.
> 
> l = Partition[Flatten[{Table[Unique[x], {n, 1, 30}]}], 3 ]
> 
> above generates a list of 10 lists with 3 elements in each as in...
> 
> {
> {x$299, x$300, x$301}, {x$302, x$303, x$304},
> {x$305, x$306, x$307}, {x$308, x$309, x$310},
> {x$311, x$312, x$313}, {x$314, x$315, x$316},
> {x$317, x$318, x$319}, {x$320, x$321, x$322},
> {x$323, x$324, x$325}, {x$326, x$327, x$328}
> }
> 
> Now suppose I want to use each of the list( all 10 of them) as a part
> of a function. . I want to "Apply" the function to every list(so, 10
> times in total)
> for a simple examplel let's add 2 to the lists
> 
> In[21]:= Apply[Plus@@xlist, 2]
> Out[21]= 2
> 
> that didn't work. i wanted to get was
> 
> {{x$299, x$300, x$301} + 2,
> {x$302, x$303, x$304} + 2...
> {x$326, x$327, x$328} + 2}}
> 
> then i want to give each of the results unique names and use the
> renamed list of lists as an argument in another function.
> 
> {
> uniquexname1 = {x$299, x$300, x$301} + 2,
> uniquexname2 = {x$302, x$303, x$304} + 2...
> uniquexname10 = {x$326, x$327, x$328} + 2}
> }
> 
> and
> 
> Map[Plus, xlist, 2]
> 
> just bring back the list itself.
> 
> This problem recurs for me. and I think i have problems with it
> because I just don't understand how Mathematica language works.
> 
> Reading the book an dhelp manual doesn't help me much in understanding
> what lies underneath.  Can you guys shed soem light on this with some
> simple examples that use numerical operations?
> 
> Maybe I'm asking a lot, but any and all insights are thoroughly
> appreciated.
> 
> thanks in advance.
> 
> sean


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