Re: Pattern matching question and answer

*To*: mathgroup at smc.vnet.net*Subject*: [mg63083] Re: Pattern matching question and answer*From*: "dkr" <dkrjeg at adelphia.net>*Date*: Tue, 13 Dec 2005 03:41:25 -0500 (EST)*References*: <dnir79$9ur$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

One alternative is to take full advantage of regexes by transforming your expression into a string. In[1]:= expr = x0*x^2 + x00*x0^2 + a0*y^2 + z0*z^2 + x0*Sin[x] ; I have replaced your y0 with an a0 for reasons explained below. In[4]:= Cases[expr, _^_*(x:_Symbol?(StringMatchQ[ToString[#1], RegularExpression["[xa]0"]] & ))] //InputForm Out[4]//InputForm= {x^2*x0, a0*y^2} In[5]:= StringCases[ToString[expr,InputForm], RegularExpression["\\b(\\w+\\^\\d+\\*[xa]0|[xa]0\\*\\w+\\^\\d+)\\b"]]// ToExpression//InputForm Out[5]//InputForm= {x^2*x0, a0*y^2} One drawback is that we have to be explicitly concerned about the Orderless attribute of Times, while the regular pattern matching involved in your approach takes this attribute into account automatically. Using a0 rather than y0 forced us to use alternation in the regex to account for the Orderless attribute. dkr