Re: Occurrences in Mathematica

*To*: mathgroup at smc.vnet.net*Subject*: [mg106373] Re: [mg106350] Occurrences in Mathematica*From*: Murray Eisenberg <murray at math.umass.edu>*Date*: Mon, 11 Jan 2010 05:28:04 -0500 (EST)*Organization*: Mathematics & Statistics, Univ. of Mass./Amherst*References*: <201001100828.DAA05428@smc.vnet.net>*Reply-to*: murray at math.umass.edu

Here's one way, via an example: lis = RandomChoice[Characters["abcdefghijklmnopqrstuvwxyz"], 50]; Select[Union[lis], Count[lis, #] == 2 &] Your results will vary according to what RandomChoice gives you. But the code does exactly what you asked: it selects (Select) from the unique elements of the list (Union[lis]) those elements for which the Count of their appearances in the list is 2. I make no claims for the efficiency of the code. That may depend upon the length and perhaps even the elements of your list, among other things. On 1/10/2010 3:28 AM, George wrote: > Hi, > > I have a very big list of elements and I need Mathematica to give me > only those elements which occure only once... > > Could anybody advise me please how to write the code for that? > > Thks much > George > -- Murray Eisenberg murray at math.umass.edu Mathematics & Statistics Dept. Lederle Graduate Research Tower phone 413 549-1020 (H) University of Massachusetts 413 545-2859 (W) 710 North Pleasant Street fax 413 545-1801 Amherst, MA 01003-9305

**References**:**Occurrences in Mathematica***From:*George <gtatishvili@gmail.com>