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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: [mg47836] Re: [mg47802] i don't understand mapping function over a long list
  • From: Yasvir Tesiram <yat at omrf.ouhsc.edu>
  • Date: Thu, 29 Apr 2004 00:34:06 -0400 (EDT)
  • References: <200404270847.EAA18860@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,
Your original list, (I got a little confused (isn't hard to do) between 
l and xlist. So I renamed it v.

v = Partition[Flatten[{Table[Unique[x], {n, 1, 30}]}], 3 ]

To get the form you want try

v1 = HoldForm[# + 2] & /@ v

But really, this is the same as v + 2. Check it with;

ReleaseHold[v1] == v + 2

At this point I consider each element of v1 to be uniquely named unless 
of course you have some legitimate reason for creating some different 
variable names. You can get at them using Part. That is, as you put it 
uniquename1 = Part[v1,1] or v1[[1]]. Your last query confuses me even 
more. To get the list back itself just subtract 2 from v1.
See the section Programming --> Functional Programming.

Cheers
Yas



On Apr 27, 2004, at 3:47 AM, 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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