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Re: When a string does not match itself

  • To: mathgroup at smc.vnet.net
  • Subject: [mg97202] Re: [mg97198] When a string does not match itself
  • From: Bob Hanlon <hanlonr at cox.net>
  • Date: Sun, 8 Mar 2009 05:49:38 -0500 (EST)
  • Reply-to: hanlonr at cox.net

"\" has a special meaning in strings. 
\n is new line, \t is tab, and otherwise \ is a literal directive

Print["This is \ttab and \
 newline\nliteral quote\" and literal \
 backslash\\ or \\\nat the end of a line"]

This is 	tab and newline
literal quote" and literal backslash\ or \
at the end of a line

And * is a wildcard in strings

StringMatchQ[#, "mon*ey"] & /@
 {"money", "monkey", "monk's key"}

{True,True,True}

Except when it is made literal

StringMatchQ[#, "mon\*ey"] & /@
 {"money", "monkey", "monk's key"}

{False,False,False}

StringMatchQ["\\*", "\\*"]

False

I suspect that because of the multiple special characters and how and when that they are internally evaluated, that this is comparing different expressions than what you intended.

StringMatchQ["\\", "\\"]

True

StringMatchQ["\*", "\*"]

True

StringMatchQ["\"", "\""]

True


Bob Hanlon

---- ingolf.dahl at telia.com wrote: 

=============
This is a maybe a trivial question, but I have not found the explanation in
help (I am using Mathematica 7.0.0):

 

Normally a string matches itself:

 

In[270]:= StringMatchQ["monkey", "monkey"]  

Out[270]= True

 

But 

 

In[271]:= StringMatchQ["\\*", "\\*"]  

Out[271]= False

 

Why? Compare also to

 

In[4]:= StringCases["\\*", "\\*"]   

Out[4]= {"\\*"}

 

In[267]:= StringPosition["\\*", "\\*"]  

Out[267]= {{1, 2}}

 

Best regards

 

Ingolf Dahl

Sweden

ingolf.dahl at telia.com



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