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MathGroup Archive 1996

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Re: Part

  • Subject: [mg2912] Re: [mg2890] Part
  • From: brucec (Bruce Carpenter)
  • Date: 9 Jan 1996 08:03:38 -0600
  • Approved: usenet@wri.com
  • Distribution: local
  • Newsgroups: wri.mathgroup
  • Organization: Wolfram Research, Inc.
  • Sender: mj at wri.com

>w={{1,2,3},{4,5,6},{7,8,9}}
>npos={2,1}
>
>npos is the position of the element I need.
>
>w[[npos]]
>
>does not work, as it returns the second and the first
>line.
>
>w[[ npos[[1]],npos[[2]] ]]
>
>does the wanted thing, but I would prefer a shorter and
>more general way.
>
>Hans Friedrich Steffani


Hi Hans--

Here is another way to solve your problem.  A top-level mechanism has been
provided to specify a sequence of variables:

In[9]:=

w={{1,2,3},{4,5,6},{7,8,9}};
npos={2,1};

In[11]:=
w[[##]]& @@ npos

Out[11]=
4

In a pure function, # specifies the first variable, #n specifies the nth
variable, ## the sequence of all variables, and ##n the sequence of
variables starting with the nth one.
(This is documented in Wolfram's Mathematica: A System for Doing
Mathematics by Computer.)
I am not critical of the use of Sequence to do this, I just prefer to use
documented commands when possible.

Best Regards,

Bruce Carpenter




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