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MathGroup Archive 2007

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Re: How to manipulate globals in a function?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg73728] Re: How to manipulate globals in a function?
  • From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
  • Date: Sun, 25 Feb 2007 04:46:33 -0500 (EST)
  • Organization: The Open University, Milton Keynes, UK
  • References: <erop34$94v$1@smc.vnet.net>

davisjf at gmail.com wrote:
> I am trying to write code to manipulate a global array in a function.
> How do something like this:
> 
> Moo [A_List, i_Integer] :=
> 
>       A[[i]] = 7;
> 
> Moo[A, 1]
> 
> This fails.  But, if I do this without a funciton it works.
> 
> i=1
> A[[i]] = 7
> 
> JD
> 
> 
Set the attribute HoldFirst.

In[1]:=
moo[a_, n_] := a[[n]] = 7
SetAttributes[moo, HoldFirst]
array = Table[Random[], {10}]
moo[array, 2]
array

Out[3]=
{0.291238, 0.68772, 0.596728, 0.994694, 0.556517,

   0.422771, 0.854193, 0.147855, 0.799394, 0.121512}

Out[4]=
7

Out[5]=
{0.291238, 7, 0.596728, 0.994694, 0.556517, 0.422771,

   0.854193, 0.147855, 0.799394, 0.121512}

Regards,
Jean-Marc


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