Re: Extracting a Function's Domain and Image
- To: mathgroup at smc.vnet.net
- Subject: [mg67989] Re: [mg67970] Extracting a Function's Domain and Image
- From: Bob Hanlon <hanlonr at cox.net>
- Date: Thu, 20 Jul 2006 06:04:28 -0400 (EDT)
- Reply-to: hanlonr at cox.net
- Sender: owner-wri-mathgroup at wolfram.com
Remove@f;
f[_]=0;
f["a"]=1;
f["b"]=2;
Clear@x;
h=DownValues@f ;
Cases[h,HoldPattern[f[x_]]->x,Infinity]
{a,b,_}
Bob Hanlon
---- Bruce Colletti <vze269bv at verizon.net> wrote:
> Re Mathematica 5.2.2.
>
> Why does the last line of code return {x} and not {a,b,_}, while if the f[_]=0 is struck, the answer is {a,b}?
>
> I want to extract the domain and image of a user-defined function, and tech support recommended using DownValues (pretty handy). If you have an easier approach, please share it. Thanks.
>
> Bruce
>
> Remove@f;
> f[_]=0;
> f["a"]=1;
> f["b"]=2;
> Clear@x;
> h=DownValues@f
> Cases[h,f[x_]->x,Infinity]
>
> Out[52]=
> {HoldPattern[f[a]]:>1,HoldPattern[f[
> b]]:>2,HoldPattern[f[_]]:>0}
>
> Out[53]=
> {x}
>