Re: Re: why does DownValues not return all
- To: mathgroup at smc.vnet.net
- Subject: [mg99465] Re: [mg99413] Re: [mg99369] why does DownValues not return all
- From: Bob Hanlon <hanlonr at cox.net>
- Date: Wed, 6 May 2009 05:24:41 -0400 (EDT)
- Reply-to: hanlonr at cox.net
Not much there, but enter
??SubValues
or
Information[SubValues]
Bob Hanlon
---- Michael <michael2718 at gmail.com> wrote:
=============
On Mon, May 4, 2009 at 7:01 AM, Bob Hanlon <hanlonr at cox.net> wrote:
> v = DeleteCases[
> ToExpression[Names["*Values"]],
> SingularValues];
>
> g["x"]["y"] = 1;
>
> {#, #[g]} & /@ v
It appears that the function that returns what I need is called "SubValues"=
:
In[9]:= SubValues[g]
Out[9]= {HoldPattern[g["x"]["y"]] :> 1}
This function doesn't appear to be documented very well (it doesn't
have it's own page), but it is mentioned in passing a couple of
places.
Thanks for the help!
>
> Bob Hanlon
Michael
>
> ---- Michael <michael2718 at gmail.com> wrote:
>
> =============
> I'm trying to get the functionality of "associative arrays" or "alist"
> or "hash tables" to work in Mathematica. However I'm seeing a quirk
> and I wonder if anybody can explain what is going on or suggest a
> better approach?
>
> I can define a simple associate array like so:
> f["red"]=1;
> f["blue"]=2;
> ...
> If all my parameters are strings, then I can find the "keys" to my
> alist with the following function:
> StringKeys[y_] := DownValues[y] /. {( _[y[str_String]] :> _) -> str};
> SetAttributes[StringKeys, HoldFirst];
>
> In[141]:= StringKeys[f]
>
> Out[141]= {"blue", "red"}
>
> However, if I try to define a more complex alist, I cannot find any
> way to retrieve the definition!
>
> In[142]:= g["x"]["y"] = 1;
>
> In[143]:= DownValues[g]
>
> Out[143]= {}
>
> In[144]:= UpValues[g]
>
> Out[144]= {}
>
>
> Any ideas?
>
> Thanks,
>
> Michael