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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)
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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.
>






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