Re: Sort[] accuracy problem

*To*: mathgroup at christensen.cybernetics.net*Subject*: [mg1145] Re: Sort[] accuracy problem*From*: roth at sunny.mpimf-heidelberg.mpg.de (Arnd Roth)*Date*: Wed, 17 May 1995 04:59:24 -0400*Organization*: Max-Planck-Institut fuer Medizinische Forschung

In article <3p657h$kb1 at news0.cybernetics.net> "Wm. Martin McClain" <wmm at chem.wayne.edu> writes: > Here is the kind of thing that is giving me trouble: > > In[299]:= Sort[{{5.00, 1}, {4.00, 3}, {1.00, 2}, {4.01, 1}}] > Out[299] = {{1.00, 2}, {4.00, 3}, {4.01, 1}, {5.00, 1}} > > But I would like it to treat 4.00 and 4.01 as the same for the > purposes of sorting, so that it returns the approximately > alphebetized list > > {{1.00, 2}, {4.01, 1}, {4.00, 3}, {5.00, 1}} > > where the difference between 1 and 3 is treated as more > important than the difference between 4.00 and 4.01.I tried > > Sort[list,(Round[#2*10]<Round[#1*10])&], > > but it seems to think that #n refers to the whole point {x,y}, > rather than just to x (or on the second round, just to y), so the > comparison becomes neither True nor False and no sorting is done. The first part of {x, y} is x, so let's just compare the first parts: In[1]:= list = {{5.00, 1}, {4.00, 3}, {1.00, 2}, {4.01, 1}} Out[1]= {{5., 1}, {4., 3}, {1., 2}, {4.01, 1}} In[2]:= Sort[list, Round[First[#1]*10] < Round[First[#2]*10] &] Out[8]= {{1., 2}, {4.01, 1}, {4., 3}, {5., 1}} Arnd Roth Abteilung Zellphysiologie Max-Planck-Institut fuer Medizinische Forschung Postfach 10 38 20, D-69028 Heidelberg, Germany http://sunny.mpimf-heidelberg.mpg.de/people/roth/ArndRoth.html