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MathGroup Archive 2005

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Re: a conflicting StringReplace

  • To: mathgroup at smc.vnet.net
  • Subject: [mg56317] Re: a conflicting StringReplace
  • From: dh <dh at metrohm.ch>
  • Date: Fri, 22 Apr 2005 06:22:42 -0400 (EDT)
  • References: <d47tic$578$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Hi Hui,
this exerpt from the help will calrify:
StringReplace goes through a string, testing substrings that start at 
each successive character position. On each substring, it tries in turn 
each of the transformation rules you have specified. If any of the rules 
apply, it replaces the substring, then continues to go through the 
string, starting at the character position after the end of the substring.

Sincerely, Daniel

Hui Fang wrote:
> I was teaching Mathematica in a college. In the class I was showing them 
> some built-in functions about strings. Since this is not a very 
> important issue, I didn't spend much time on each function. When I show 
> them StringReplace, I gave them the following examples:
> In[1]    StringReplace["abc",{"ab"->"AB"}]
> Out[1]   ABc
> 
> In[2]   StringReplace["abc", {"bc"->"BC"}]
> Out[2]   aBC
> 
> No problem on those. Now a student tried the following:
> In[3]   StringReplace["abc", {"ab"->"AB", "bc"->"BC"}]
> Out[3]   ABc
> 
> Now he asked me why only "ab" is replaced. I said this is because there 
> is a conflict because both "ab" and "bc" contains "b". So Mathematica 
> will choose the first replacement. I also told him if he changes the 
> order, he will get aBC. Now:
> In[4]    StringReplace["abc", {"bc"->"BC","ab"->"AB"}]
> Out[4]    ABc
> 
> This is the part I don't understand. Does Mathematica treat those rules 
> in their canonical order (since "ab" is before "bc" in canonical 
> order.), or in their written order?
> 
> Thanks a lot!
> 
> Hui Fang      
> 


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