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MathGroup Archive 2005

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Re: String comparison

  • To: mathgroup at smc.vnet.net
  • Subject: [mg55022] Re: String comparison
  • From: Peter Pein <petsie at arcor.de>
  • Date: Thu, 10 Mar 2005 05:24:21 -0500 (EST)
  • References: <d0mo83$755$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

yasdfer at yahoo.com wrote:
> Hi,
> 
> I want to sort a list/table based on an arbitrary "column".
> 
> In[1]:= alist = {{a, 3, "bca"}, {b, 1, "cba"}, {c, 2, "abc"}};
> 
> If I want to sort based on say the second column, I can use:
> 
> In[2]:= Sort[alist, #1[[2]] > #2[[2]] &]
> Out[2]:= {{a, 3, bca}, {c, 2, abc}, {b, 1, cba}}
> 
> With the string column however, the method fails:
> 
> In[3]:= Sort[alist, #1[[3]] > #2[[3]] &]
> Out[3]:= {{a, 3, bca}, {b, 1, cba}, {c, 2, abc}}
> 
> I can get away with,
> 
> In[4]:= Reverse[RotateRight[#, 2] & /@ Sort[RotateLeft[#, 2] & /@
> alist]]
> Out[4]:= {{b, 1, cba}, {a, 3, bca}, {c, 2, abc}}
> 
> Question is, what function can I pass to Sort[] directly to avoid the
> bending and twisting?
> 
> In general, how does one compare strings for lexical ordering? Noticed
> that, Greater["a", "b"] does not evaluate either.
> 
> Thanks.
> 

alist={{a,3,"bca"},{b,1,"cba"},{c,2,"abc"}};

to get the reverse alphabetical order as in your exanple:
In[2]:= Sort[alist,OrderedQ[Last/@{#2,#1}]&]
Out[2]= {{b,1,cba},{a,3,bca},{c,2,abc}}

Look for "Sorting" in the documentation => Sorting of strings =>
Mathematica Book 2.8.2
-- 
Peter Pein
Berlin


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