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MathGroup Archive 1999

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Re: easiest way to sort a list?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg18320] Re: [mg18308] easiest way to sort a list?
  • From: "ARNOLDK" <arnoldk at gauss.cam.wits.ac.za>
  • Date: Sat, 26 Jun 1999 19:08:01 -0400
  • Sender: owner-wri-mathgroup at wolfram.com



>Hi everyone,
>
>Here's my question:  Suppose you have a list of integers, not all distinct,
>say
>      {1, 5, 3, 5, 10, 10, 1},
>
>and you want to obtain the list
>
>      {1, 5, 3, 10}
>
>which is the set of distinct elements but with the order preserved.

Here's one way
In[5]:=
{1, 5, 3, 5, 10, 10, 1,4,4}
//.{a___,b_,c___,b_,d___}->{a,b,c,d}

Out[5]=
{1,5,3,10,4}

Or try this

 In[20]:=
union2[l_]:=Fold[Flatten[If[!MemberQ[#1,#2],Append[#1,#2],#1]]&,{},l
]
In[21]:=
union2[{1, 5, 3, 5, 10, 10, 1,4,4}]

Out[21]=
{1,5,3,10,4}

Arnold Knopfmacher
Wits University
South Africa



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