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Nov 23rd, 2007

How to check element of list are present in other list?

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Hi,

I have two list of any datatype supported by python. I want to check whether the any of the element of first list
is present in second list or not.

Example: I have
a = [4,5,6]
b = [1,3,8,6,7,9]

I want to check whether any element of a is present in be or not. Also without using for loop.
Is there any other way to do this or any inbuilt function of python,which will check this. Please suggest me.

Thanks

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R.S.Chourasia

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Newbie Poster

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Nov 24th, 2007

Re: How to check element of list are present in other list?

Convert them to sets and use the intersection.

woooee

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Nearly a Posting Maven

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Nov 26th, 2007

Re: How to check element of list are present in other list?

Hello,

Thanks for your reply.
Since I am new to python, i do not have any idea of sets. So It would be good for me if you can give me an example of, how to it convert in to sets and how to take the intersection.

Thanks

R.S.Chourasia

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Nov 26th, 2007

Re: How to check element of list are present in other list?

Python Syntax (Toggle Plain Text)
a = [4,5,6]
s = set(a)
a = [4,5,6]
s = set(a)

Now s is a set

For further info have a look at the documentation.

Last edited by mawe; Nov 26th, 2007 at 9:31 am.

mawe

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Junior Poster

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Nov 26th, 2007

Re: How to check element of list are present in other list?

Actually there are many ways to solve this, but here would be an example for a beginning student. Study it and try to understand it ...

python Syntax (Toggle Plain Text)
a = [4,5,6]
b = [1,3,8,6,7,9]
 
c = []
for bx in b:
    if bx in a:
        c.append(bx)
 
if c:
    print "these are the elements of list a that are present in list b:"
    print c
else:
    print "no elements of list a are in list b"
a = [4,5,6]
b = [1,3,8,6,7,9]

c = []
for bx in b:
    if bx in a:
        c.append(bx)
        
if c:
    print "these are the elements of list a that are present in list b:"
    print c
else:
    print "no elements of list a are in list b"

vegaseat

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DaniWeb's Hypocrite

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Nov 26th, 2007

Re: How to check element of list are present in other list?

Nice and easy, vegaseat, but

Quote originally posted by R.S.Chourasia ...

Also without using for loop.

mawe

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Nov 24th, 2008

Re: How to check element of list are present in other list?

Here is the answer to do the same ...using sets..

from sets import Set
a = Set([1,2,3,4,5])
b = Set([6,7,8,9,10])
c = Set([2,4,6,8,10])
s1 = list(a.intersection(b))
s2 = list(a.intersection(c))
s3 = list(b.intersection(c))
print s1
print s2
print s3

R.S.Chourasia

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Feb 26th, 2009

Re: How to check element of list are present in other list?

This following if condition to check for the presence of an element in a list is just wonderful.

if bx in b:

where bx is a element that can be checked for its presence in the list b

Thank you,

systemsbiology

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