# [Tutor] finding non unique data in lists

Kent Johnson kent_johnson at skillsoft.com
Thu Oct 14 13:44:55 CEST 2004

Scott,

You can make a Set from each list, then find the intersection of all the
sets. That will contain just the elements in all the lists.

>>> from sets import Set

First some raw data:
>>> l1 = [1,2,3,4,5,6,7]
>>> l2 = [2,3,4,7]
>>> l3 = [1,2,3,5,6,7]

Sets can be constructed from lists:
>>> s1 = Set(l1)
>>> s1
Set([1, 2, 3, 4, 5, 6, 7])
>>> s2 = Set(l2)
>>> s3 = Set(l3)

Sets overload the & operator to mean set intersection:
>>> all = s1 & s2 & s3
>>> all
Set([2, 3, 7])

Sets allow iteration to process their elements one-by-one:
>>> for i in all:
...   print i
...
2
3
7

http://docs.python.org/lib/module-sets.html

Kent

At 01:12 PM 10/14/2004 +0200, Scott Melnyk wrote:
>Hello!
>
>I have a collection of lists of different lengths (containing exons
>from genetic data) that I would like to compare and only keep the
>those that are found within each of the lists.  Any exon not present
>in all the lists is not important to me.
>
>I am new to python and was told that sets could be used easily to find
>the unique data but I am unsure the most efficient way how to pull out
>the non-unique data.
>
>All suggestions are very much appreciated and welcome.
>
>
>--
>Scott
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