Re: Subsetting indexed variable?
- To: mathgroup at smc.vnet.net
- Subject: [mg36071] Re: Subsetting indexed variable?
- From: "Ersek, Ted R" <ErsekTR at navair.navy.mil>
- Date: Thu, 15 Aug 2002 02:36:23 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
Below I slightly modify a problem Gareth Russell had. I modified it to
avoid confusion on how to generalize the solution to a different example.
------
suppose we have:
b[1,3] = 3;
b[0,6] = 6;
b[5678, 3] = 7;
b[5678, 4] = 5;
Then how can we get a list of what (b) can return when the first argument
is (5678).
In this example we want to get {7,5}. The solution is to use the
following:
In[5]:=
posn=Position[DownValues[b], b[5678,_] ];
Extract[DownValues[b], {First[#],2}& /@ posn ]
Out[6]=
{7,5}
--------
Let myself or the mathgroup know if you have trouble understanding
{First[#],2}& /@ posn
--------
The solution above works because the definitions for (b) are stored in
DownValues[b].
You can see the definitions if you evaluate the following.
In[7]:=
DownValues[b]
--------
Regards,
Ted Ersek
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