Re: Sort problem

*To*: mathgroup at smc.vnet.net*Subject*: [mg81722] Re: Sort problem*From*: mcmcclur at unca.edu*Date*: Tue, 2 Oct 2007 05:38:13 -0400 (EDT)*References*: <fdqd33$n6m$1@smc.vnet.net>

On Oct 1, 5:02 am, Donald DuBois <don... at comcast.net> wrote: > 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}} According to the documentation, the default ordering function for Sort is OrderedQ[{#1,#2}]& (as opposed to Less, which you use). Thus, to emulate this behavior with the restriction to the first element, you could use: Sort[{{r, 2}, {a, 3}, {x, 4}}, OrderedQ[{#1[[1]], #2[[1]]}] &] Conversely, you could force the more confusing behavior in the first example by switching the input to Sort[{r, a, x}, #1 < #2 &] I suppose the reason is that Less compares numerical quantities, while OrderedQ is more general. Mark