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Re: why does DownValues not return all downvalues for a

  • To: mathgroup at smc.vnet.net
  • Subject: [mg99413] Re: [mg99369] why does DownValues not return all downvalues for a
  • From: Michael <michael2718 at gmail.com>
  • Date: Tue, 5 May 2009 05:41:59 -0400 (EDT)
  • References: <200905040959.FAA22619@smc.vnet.net>

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


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