Re: Sort problem

*To*: mathgroup at smc.vnet.net*Subject*: [mg81743] Re: Sort problem*From*: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>*Date*: Tue, 2 Oct 2007 05:49:03 -0400 (EDT)*Organization*: The Open University, Milton Keynes, UK*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? Using inequalities on purely alphabetic symbol. Use either nothing (as long as you want the list sorted according to its first column) or *OrderedQ* as in the following examples. In[1]:= Sort[{{r, 2}, {a, 3}, {x, 4}}] Out[1]= {{a, 3}, {r, 2}, {x, 4}} In[2]:= Sort[{{r, 2}, {a, 3}, {x, 4}}, OrderedQ[{#1[[1]], #2[[1]]}] &] Out[2]= {{a, 3}, {r, 2}, {x, 4}} Regards, -- Jean-Marc