Deleting a DownValue, Evaluate[f@@argList]=. does not do it
- To: mathgroup at smc.vnet.net
- Subject: [mg20744] Deleting a DownValue, Evaluate[f@@argList]=. does not do it
- From: hanssen at zeiss.de
- Date: Wed, 10 Nov 1999 00:17:53 -0500
- Sender: owner-wri-mathgroup at wolfram.com
Hi, MathGroup,
f[1]=1;
f[2]=2;
?f
yields
"Global`f"
f[1] = 1
f[2] = 2
now get rid of definition for 1
f[1]=.;
?f
yields
"Global`f"
f[2] = 2
So far, it works as expected. I want to memorize results for combinations of arguments
like f[a,b,c]=results and so on. To do this, I write f@@argList. Now I demonstrate
this on lists with length 1, to make it simple. When making the assignment, it has to be
wrapped in Evaluate:
Clear[f];
Evaluate[f@@{1}]=1;
Evaluate[f@@{2}]=2;
?f
yields
"Global`f"
f[1] = 1
f[2] = 2
as before. Now I want to get rid of the definition for 1 in the analogous way:
Evaluate[f@@{1}]=.
yields
Unset::usraw: Cannot unset raw object !
$Failed
How to proceed without searching through DownValues[f] and deleting
the one meant - very awkward?
kind regards
Dipl.-Math. Adalbert Hanszen