Re: String comparison
- To: mathgroup at smc.vnet.net
- Subject: [mg55034] Re: [mg55009] String comparison
- From: "Christoph Lhotka" <lhotka at astro.univie.ac.at>
- Date: Thu, 10 Mar 2005 05:24:38 -0500 (EST)
- Sender: owner-wri-mathgroup at wolfram.com
Hi,
The solution to your problem ist the function OrderedQ:
In[..]:=Sort[alist, OrderedQ[{#1[[3]], #2[[3]]}] &]
Out[..]:={{c, 2, abc}, {a, 3, bca}, {b, 1, cba}}
OrderedQ[{a,b}] returns true, if a and b are in lexikograohic order, and false
otherwise, you can use it for strings and expressions:
In[..]:=OrderedQ[{b,a}]
Out[..]:=False
In[..]:=OrderedQ[{"a","b"}]
Out[..]:=True
with kind regards ...
On Wed, 9 Mar 2005 06:34:34 -0500 (EST)
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.
>
-- Christoph Lhotka --
University of Vienna
Institute for Astronomy
Tuerkenschanzstr. 17
1180 Vienna, Austria
fon. +43.1.4277.518.41
mail. lhotka at astro.univie.ac.at