Re: Deleting more subtle then Clear[ ] ?
- Subject: [mg2239] Re: Deleting more subtle then Clear[ ] ?
- From: wagner at bullwinkle.cs.Colorado.EDU (Dave Wagner)
- Date: Wed, 18 Oct 1995 05:54:06 GMT
- Approved: usenet@wri.com
- Distribution: local
- Newsgroups: wri.mathgroup
- Organization: University of Colorado, Boulder
- Sender: daemon at wri.com ( )
In article <DGJqH7.BqD at wri.com>, <alfred at ca-risc.co.at> wrote: > >Well, > Let's assume we have a function f[x,y,z] where x and y are VERY big or >time consuming lists of numbers or functions. > By defining f[x_,y_,z_]:= f[x,y,z] = I make MMA remember what it did. >How can I now tell it to disremember for all f[x,*,*] when I specifically want >it to reprocess whatever is dependend on x (i.e. the contents of the file has >changed but the name is the same) but NOT on y? I'm not sure you can do what you want to do, but maybe I misunderstand what you are trying to do. If what you mean is that you want to delete all definitions containing a certain value for x, you can do it as follows: First, some example definitions. In[1]:= f[x_, y_, z_] := f[x, y, z] = x + y + z f[1,2,3]; f[2,3,4]; f[1,3,5]; The definitions for f are stored in DownValues[f]. In[5]:= DownValues[f] Out[5]= {Literal[f[1, 2, 3]] :> 6, Literal[f[1, 3, 5]] :> 9, Literal[f[2, 3, 4]] :> 9, Literal[f[x_, y_, z_]] :> (f[x, y, z] = x + y + z)} You can use DeleteCases to remove all definitions whose left-hand side depends on a particular value of x as follows: In[8]:= DownValues[f] = DeleteCases[DownValues[f], Literal[_[f[1,__]] :> _]] Out[8]= {Literal[f[2, 3, 4]] :> 9, Literal[f[x_, y_, z_]] :> (f[x, y, z] = x + y + z)} In this case, I have removed all rules for f[1, *, *] (to use your notation) but left the others intact. Note the weird pattern used as the second argument to DeleteCases. First of all, the entire thing has to be wrapped in Literal or else DeleteCases will interpret it as a replacement rule, rather than a pattern that matches a replacement rule. Also note that each left-hand side of DownValues[f] is wrapped in Literal, which is impossible to match (because the pattern matcher ignores it); hence we simply match _[f[1, __]]. I hope this is what you're trying to do. Dave Wagner Principia Consulting (303) 786-8371 dbwagner at princon.com http://www.princon.com/princon