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Deleting Selective DownValues

• To: mathgroup at smc.vnet.net
• Subject: [mg63985] Deleting Selective DownValues
• From: "David Park" <djmp at earthlink.net>
• Date: Thu, 26 Jan 2006 03:43:12 -0500 (EST)
• Sender: owner-wri-mathgroup at wolfram.com

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/ 

• Follow-Ups:
  • Re: Deleting Selective DownValues
    • From: "Carl K. Woll" <carlw@wolfram.com>