Re: Exercise of Programming with Mathematica

*To*: mathgroup at smc.vnet.net*Subject*: [mg131868] Re: Exercise of Programming with Mathematica*From*: Helen Read <readhpr at gmail.com>*Date*: Sun, 20 Oct 2013 23:39:06 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*Delivered-to*: l-mathgroup@wolfram.com*Delivered-to*: mathgroup-outx@smc.vnet.net*Delivered-to*: mathgroup-newsendx@smc.vnet.net*References*: <l3qrmm$3ps$1@smc.vnet.net>

How about: Map[Reverse, {{a, b}, {c, d}, {e, f}}] Map[Reverse, {{a, b}, {c, d}}] Helen Read University of Vermont On 10/18/2013 4:32 AM, Zhenyi Zhang wrote: > Here is a rule designed to switch the order of each pair of expressions in a list. It works fine on the > first example, but fails on the second. > In[1]:= {{a, b}, {c, d}, {e, f}}/.{x_, y_} :> {y, x} > Out[1]= {{b, a}, {d, c}, {f, e}} > In[2]:= {{a, b}, {c, d}}/.{x_, y_} :> {y, x} > Out[2]= {{c, d}, {a, b}} > Explain what has gone wrong and rewrite this rule to correct the situation, that is, so that the second > example returns {{b, a}, {d, c}} > > My solution is the most stupid one. > > {{a, b}, {c, d}}/.{{x_, y_}, {w_, t_}} :> {{y, x}, {t, w}} > > May I ask any elegant solutions? > > Thanks. >