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Re: Deleting Selective DownValues

• To: mathgroup at smc.vnet.net
• Subject: [mg64007] Re: [mg63985] Deleting Selective DownValues
• From: "Carl K. Woll" <carlw at wolfram.com>
• Date: Fri, 27 Jan 2006 05:13:18 -0500 (EST)
• References: <200601260843.DAA22213@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

David Park wrote:
> I think I found the solution for deleting definitions with a given number of arguments. The trick was to change the function name to stop evaluation.
> 
> deleteDownValue[label_Symbol, numberOfArgs_Integer?Positive] :=
>   Module[{g},
>     DownValues[f] =
>         Select[DownValues[f], 
>           Length[First[#] /. label -> g /. HoldPattern -> Identity] != 
>               numberOfArgs &];]
> 
> Clear[f]
> f[x_, y_, z_] := x y z
> f[a_, b_] := a b
> f[x_] := x
> DownValues[f]
> deleteDownValue[f, 2]
> DownValues[f]
> 
> {HoldPattern[f[x_, y_, z_]] :> x y z, HoldPattern[f[a_, b_]] :> a b, 
>   HoldPattern[f[x_]] :> x}
> 
> {HoldPattern[f[x_, y_, z_]] :> x y z, HoldPattern[f[x_]] :> x}
> 
> David Park
> djmp at earthlink.net
> http://home.earthlink.net/~djmp/ 

David,

Here's another idea:

deletedv[f_, n_] := DownValues[f] = DeleteCases[DownValues[f],
     (Verbatim[HoldPattern][_[x__]] :> _)
      /; Length[{x}] == n]

Carl Woll
Wolfram Research

• References:
  • Deleting Selective DownValues
    • From: "David Park" <djmp@earthlink.net>