Re: a conflicting StringReplace
- To: mathgroup at smc.vnet.net
- Subject: [mg56336] Re: [mg56306] a conflicting StringReplace
- From: Igor Antonio <igora at wolf-ram.com>
- Date: Fri, 22 Apr 2005 06:23:21 -0400 (EDT)
- References: <200504210936.FAA05094@smc.vnet.net>
- Reply-to: igora at wolf-ram.com
- Sender: owner-wri-mathgroup at wolfram.com
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
Hui,
This behavior is correct. This excerpt is from the documentation:
=========
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.
=========
It will test all of the rules in the list before moving on to the next
character in the string.
--
Igor Antonio
Wolfram Research, Inc.
http://www.wolfram.com
To email me personally, remove the dash.
- References:
- a conflicting StringReplace
- From: Hui Fang <fangh73@xmu.edu.cn>
- a conflicting StringReplace