Re: Help with Hold
- To: mathgroup at smc.vnet.net
- Subject: [mg100933] Re: [mg100917] Help with Hold
- From: John Fultz <jfultz at wolfram.com>
- Date: Thu, 18 Jun 2009 06:18:27 -0400 (EDT)
- Reply-to: jfultz at wolfram.com
On Thu, 18 Jun 2009 04:52:55 -0400 (EDT), Erich Neuwirth wrote: > How can I transform > > Hold[x,Null,y,Null,Null] > into > {"x",Null,"y",Null,Null} > even if x and/or y have assigned values? Not sure if this is the most concise/clever way, but it certainly works. I assume here that your criteria for choosing 'x' and 'y', but not 'Null' is that 'x' and 'y' are symbols and in the Global` context. isGlobalSymbol[x_Symbol] := Context[x] === "Global`"; isGlobalSymbol[x_] := False; SetAttributes[isGlobalSymbol, HoldAll]; List @@ (Hold[x, Null, y, Null, Null] /. var_?isGlobalSymbol :> ToString[Unevaluated[var]]) Sincerely, John Fultz jfultz at wolfram.com User Interface Group Wolfram Research, Inc.
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