Re: Challenge!

*To*: mathgroup at christensen.cybernetics.net*Subject*: [mg922] Re: Challenge!*From*: Gennady <stupakov at slac.stanford.edu>*Date*: Wed, 3 May 1995 00:01:08 -0400*Organization*: SLAC

In article <3nkc03$mq8 at news0.cybernetics.net> Paul E Howland, PEHOWLAND at taz.dra.hmg.gb writes: >Dear Mathgroup, > >I have two lists of equal length M. > >I wish to generate a third list also of length M, where the i th element >of this list is either the i th element of the first list, or the i th >element of the second list. > >It should be equally probable that the new element be chosen from the >first or second list. > >eg. I have a list {a,b,c,d,e,f,g} > and another {A,B,C,D,E,F,G} > >valid answers would be: > {a,B,C,d,e,F,G} > {a,b,c,d,E,f,g} > {A,B,C,D,e,f,G} > etc. > >The function I have written to do this is: > > swap[list1_List, list2_List] := > Module[{newlist={},M}, > M = Length[list1]; > Do [AppendTo[ > newlist, > If[Random[]>0.5, list1[[i]], list2[[i]]] > ], > {i, M} > ]; > newlist > ] > >which works fine, but it really isn't very elegant in terms of Mathematica's >functional programming style. There must be a more compact way to do this >in terms of Mapping functions, and so on. > >What is the most compact function that could achieve my goal? > >Paul. > > Here is a shorter way to do the job: In[18]:= l1={a,b,c,d,e,f,g}; l2={A,B,C,D,E,F,G}; In[47]:= swap[l1_,l2_]:=Map[Part[#,Random[Integer,{1,2}]]&, Transpose[{l1,l2}]]//Flatten In[48]:= swap[l1,l2] Out[48]= {A, b, C, d, E, F, g} In[49]:= swap[l1,l2] Out[49]= {a, b, C, d, e, f, G} Regards, Gennady.