Re: Call-by-reference from inside a function
- To: mathgroup at smc.vnet.net
- Subject: [mg72598] Re: Call-by-reference from inside a function
- From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
- Date: Wed, 10 Jan 2007 04:20:24 -0500 (EST)
- Organization: Uni Leipzig
- References: <eo012n$kp1$1@smc.vnet.net>
- Reply-to: kuska at informatik.uni-leipzig.de
Hi, and SetAttributes[RandomChoseElem, HoldAll] RandomChoseElem[list_] := Module[{pos, elem}, pos = Random[Integer, {1, Length[list]}]; elem = list[[pos]]; list = Drop[list, {pos}]; elem ] does what you want. Regards Jens 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] >