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Re: Extract values and multilpicities from list

• To: mathgroup at smc.vnet.net
• Subject: [mg64872] Re: [mg64849] Extract values and multilpicities from list
• From: Pratik Desai <pdesai1 at umbc.edu>
• Date: Mon, 6 Mar 2006 05:01:26 -0500 (EST)
• References: <200603050819.DAA09793@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

Dr. Wolfgang Hintze wrote:

>Given a list of integers which may repeat, e.g.
>
>lstIn = {2,3,4,4,2,1,1,5,4}
>
>provide a list of different values and their respective multiplicities,
>in the example,
>
>LstOut= {{1,2},{2,2},{3,1},{4,3},{5,1}}
>
>Who finds the shortest function doing this task in general?
>
>Thanks.
>
>Best regards,
>Wolfgang
>
>  
>
Here is one such attempt

In[1]:=
Clear[list1,CommonVals,data]
CommonVals[list_?ListQ]:=Module[{list1=list},Table[{Union[list1][[r]],Count[list1,Union[list1][[r]]]},{r,1,Length[Union[list1]]}]]
list1 = {2,3,4,4,2,1,1,5,4}
CommonVals[list1]//Timing
data=Table[Random[Integer, {1, 9}], {10^5}];
CommonVals[data]//Timing


Out[3]=
{2,3,4,4,2,1,1,5,4}

Out[4]=
{0. Second,{{1,2},{2,2},{3,1},{4,3},{5,1}}}

Out[6]=
{0.771 Second,{{1,11091},{2,
  10991},{3,11107},{4,11175},{5,11022},{6,11133},{7,11098},{8,11194},{
      9,11189}}}

• References:
  • Extract values and multilpicities from list
    • From: "Dr. Wolfgang Hintze" <weh@snafu.de>