Re: Part
- To: mathgroup at smc.vnet.net
- Subject: [mg2912] Re: [mg2890] Part
- From: brucec (Bruce Carpenter)
- Date: Tue, 9 Jan 1996 02:18:54 -0500
>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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