Re: Help with Hold

*To*: mathgroup at smc.vnet.net*Subject*: [mg100976] Re: Help with Hold*From*: Peter Breitfeld <phbrf at t-online.de>*Date*: Thu, 18 Jun 2009 20:50:28 -0400 (EDT)*References*: <h1cv8s$jfg$1@smc.vnet.net>

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? > Do you want something like this: stringList[expr_]:= List @@ Fold[ReplacePart[#1, #2 -> Extract[#1, #2, ToString]] &, expr, Reverse[Sort[pos]]] // InputForm Clear[x,y] hh=Hold[x,Null,y,Null,Null] In= stringList[hh] Out={"x", "Null", "y", "Null", Null} In= y=2; stringLst[hh] Out={"x", "Null", "2", "Null", Null} -- _________________________________________________________________ Peter Breitfeld, Bad Saulgau, Germany -- http://www.pBreitfeld.de