Re: SortBy won't order irrationals

*To*: mathgroup at smc.vnet.net*Subject*: [mg124055] Re: SortBy won't order irrationals*From*: "Sjoerd C. de Vries" <sjoerd.c.devries at gmail.com>*Date*: Sat, 7 Jan 2012 05:21:33 -0500 (EST)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*References*: <je6e9b$q93$1@smc.vnet.net>

This behavior is precisely as described in the documentation: "Sort treats powers and products specially, ordering them to correspond to terms in a polynomial." FullForm[Sqrt[2]] => Power[2,Rational[1,2]] Adding an N to your SortBy function isn't that much of a trouble is it? In case of Sort you could use Less as the ordering function. Cheers -- Sjoerd Check out Stackoverflow's Mathematica tag: http://stackoverflow.com/questions/tagged/mathematica or better, help out with the new dedicated Mathematica Q&A site on StackExchange. It's almost in private beta, but needs just a few extra people to kick off and participate. Go to: http://area51.stackexchange.com/proposals/37304/mathematica?referrer=EJOMFcZOBpAIDM_ 9uBjtlA2 On Jan 6, 10:18 am, Chris Young <c... at comcast.net> wrote: > Have to use N[ ] on them first. Combined with Sort's refusal to accept > multiple keys, this is extremely exasperating. > > In[1218]:= ptsIrr = > { > {0, 2}, {1, Sqrt[2]}, {2, 2}, > {4, 1}, {Sqrt[5], 1}, {6, 1}, {Sqrt[3], 1}, > {7, 0}, {-1, 0} > } > > Out[1218]= {{0, 2}, {1, Sqrt[2]}, {2, 2}, {4, 1}, {Sqrt[5], 1}, {6, > 1}, {Sqrt[3], 1}, {7, 0}, {-1, 0}} > > In[1219]:= sortIrrY = SortBy[ptsIrr, #[[2]] &] > > Out[1219]= {{-1, 0}, {7, 0}, {4, 1}, {6, 1}, {Sqrt[3], 1}, {Sqrt[5], > 1}, {0, 2}, {2, 2}, {1, Sqrt[2]}} > > In[1220]:= sortIrrYN = SortBy[ptsIrr // N, #[[2]] &] > > Out[1220]= {{-1., 0.}, {7., 0.}, {1.73205, 1.}, {2.23607, 1.}, {4., > 1.}, {6., 1.}, {1., 1.41421}, {0., 2.}, {2., 2.}} > > In[1221]:= sortIrrYN2 = SortBy[ptsIrr, N[#[[2]]] &] > > Out[1221]= {{-1, 0}, {7, 0}, {4, 1}, {6, 1}, {Sqrt[3], 1}, {Sqrt[5], > 1}, {1, Sqrt[2]}, {0, 2}, {2, 2}}