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