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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: [mg47840] RE: [mg47802] i don't understand mapping function over a long list
  • From: "tgarza01 at prodigy.net.mx" <tgarza01 at prodigy.net.mx>
  • Date: Thu, 29 Apr 2004 00:34:29 -0400 (EDT)
  • Reply-to: tgarza01 at prodigy.net.mx
  • Sender: owner-wri-mathgroup at wolfram.com

For one thing, xlist is not defined (your list is called l).
And you can't get

{{x$299 + 2, x$300 + 2, x$301 +2},
{x$302 + 2, x$303 + 2, x$304 + 2}...

{x$326 + 2, x$327 + 2, x$328 + 2}}}

as the output of any evaluation. Mathematica will always give 

{{x$299 + 2, x$300 + 2, x$301 +2},
{x$302 + 2, x$303 + 2, x$304 + 2}...

{x$326 + 2, x$327 + 2, x$328 + 2}}}

since adding any constant to a list will result in adding that constant to
each element of the list.

Tomas Garza
Mexico City
 

Original Message:
-----------------
From:  sean_incali at yahoo.com (sean kim)
To: mathgroup at smc.vnet.net
Subject: [mg47840] [mg47802] i don't understand mapping function over a long list


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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