Re: Call-by-reference from inside a function
- To: mathgroup at smc.vnet.net
- Subject: [mg72579] Re: [mg72568] Call-by-reference from inside a function
- From: János <janos.lobb at yale.edu>
- Date: Wed, 10 Jan 2007 03:03:02 -0500 (EST)
- References: <200701091249.HAA21706@smc.vnet.net>
On Jan 9, 2007, at 7:49 AM, zac wrote:
> 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]
In my humble newbie opinion, you either do not need a scoping Module
there, or if you do, then you can return a two element list where the
first member is the dropped element and the second one is the
modified list.
RandomChoseElem[list_List] := Module[
> {pos, elem, mlist},
> pos = Random[Integer, {1, Length[list]}];
> elem = list[[pos]];
> mlist = Drop[list, {pos}];
> Return[{elem,mlist}]
> ];
>
and then the call would look like:
sss=RandomChoseElem[set]
set=Last[sss];
dropped_element=First[sss];
Csóka családnak,
János
- References:
- Call-by-reference from inside a function
- From: "zac" <replicatorzed@gmail.com>
- Call-by-reference from inside a function