Re: Selecting dynamically from a list
- To: mathgroup at smc.vnet.net
- Subject: [mg84706] Re: Selecting dynamically from a list
- From: dh <dh at metrohm.ch>
- Date: Thu, 10 Jan 2008 05:36:17 -0500 (EST)
- References: <fm4hcd$6ts$1@smc.vnet.net>
Hi John
using FullForm you can see what you get. E.g.:
choosein[mylist]//FullForm will show you that the return value is
Dynamic[..], not a value you can easily calulate with. However you have
a real problem. If you get rid of the "Dynamic" you have a problem.
Because, when you write var=choosein, the assignement is done once and
not updated later. A possible solution would be to feed the variable to
choosein, e.g.:
choosein[myl_List,myVar_Symbol] := Module[{mychoice1 = {}},
Print[CheckboxBar[Dynamic@mychoice1, myl]];
myVar:=Setting[mychoice1]]
Note the delayed assignment that ensures the updating.
hope this helps, Daniel
John Jowett wrote:
> Hello,
> While writing this post, I found the solution myself. At the
> risk of making myself look a bit slow, let me communicate it anyway.
> Conceivably it may help someone else who doesn't find the solution
> obvious.
>
> I have an application where, in essence, I would like to visually pick
> a few values out of a list to make a new list. I can do it at a basic
> level with
>
> mylist = {a, b, c, d, e, f};
>
> CheckboxBar[Dynamic[mychoice0], mylist]
>
> which displays a row of check boxes. After picking a couple I find
> that the variable mychoice0 has simply been assigned a value {a,c,e},
> for example. I can then go on and calculate other things with it,
> e.g.,
>
> Length[mychoice0] which returns 2.
>
> So far, so good. Then I try to build on that, by writing a function
> to pick from an arbitrary list. After some trial and error, I came up
> with
>
>
> choosein[myl_List] := Module[{mychoice1 = {}},
> Print[CheckboxBar[Dynamic@mychoice1, myl]];
> Dynamic[mychoice1]]
>
> and try it out with
>
> myc = choosein[mylist]
>
> Sure enough this displays an output corresponding to my choice from
> the check boxes. However if I try to do anything else with the
> variable myc, I quickly find out that it is not what it appears to be
> and cannot be used in calculations. This was puzzling until I
> discovered that
>
> myc1 = Setting[myc]
>
> will give the list I wanted. However it is NOT possible to
> incorporate the call to Setting in the definition of the function
> choosein.
>
> Can anyone improve on this approach ?
>
> John Jowett
>
>