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MathGroup Archive 2007

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RE: Call-by-reference from inside a function

  • To: mathgroup at smc.vnet.net
  • Subject: [mg72573] RE: [mg72568] Call-by-reference from inside a function
  • From: "David Park" <djmp at earthlink.net>
  • Date: Wed, 10 Jan 2007 02:38:56 -0500 (EST)

Give your function the Attribute HoldFirst.

David Park
djmp at earthlink.net
http://home.earthlink.net/~djmp/ 

From: zac [mailto:replicatorzed at gmail.com]


Dear Group,

I'm in need of a function, which is called with one argument, a list.
The function is to chose one element of the list randomly, AND modify
the original list by removing the chosen element from it. My problem is
that I cannot modify the global variable from inside the function. It
is not a solution to return with a list such as:
Return[{chosen_element, modified_local_list}], and than make an
assignment outside the function.
I'm thinking on some call-by-reference method, but as I've learned so
far, there is no user-friendly way to do this, just some workarounds
(which I don't know). Any suggestions?

Istvan

example code below:

RandomChoseElem[list_List] := Module[
      {pos, elem},
      pos = Random[Integer, {1, Length[list]}];
      elem = list[[pos]];
      (* This is to be solved inside : *)
      (* global`list = Drop[global`list, {pos}]; *)
      Return[elem]
      ];

set = {1, 2, 3, 4};

RandomChoseElem[set]



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