Re: Sort problem
- To: mathgroup at smc.vnet.net
- Subject: [mg81739] Re: Sort problem
- From: Szabolcs Horvát <szhorvat at gmail.com>
- Date: Tue, 2 Oct 2007 05:46:59 -0400 (EDT)
- References: <fdqd33$n6m$1@smc.vnet.net>
Donald DuBois wrote:
> Hello,
>
> This Sort works
>
> In[32]:= Sort[{r, a, x}]
>
> Out[32]= {a, r, x}
>
> but this one doesn't:
>
> In[33]:= Sort[{{r, 2}, {a, 3}, {x, 4}}, #1[[1]] < #2[[1]] &]
>
> Out[33]= {{r, 2}, {a, 3}, {x, 4}}
>
>
> What am I doing wrong?
>
This is because "r < a" does not evaluate to False or True. You don't
need anything special to make Sort[] work in this example:
In[1]:= Sort[{{r, 2}, {a, 3}, {x, 4}}]
Out[1]= {{a, 3}, {r, 2}, {x, 4}}
The correct version of In[33] from your message would be:
In[2]:= Sort[{{r, 2}, {a, 3}, {x, 4}}, OrderedQ[{#1[[1]], #2[[1]]}] & ]
Out[2]= {{a, 3}, {r, 2}, {x, 4}}
--
Szabolcs