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

```

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