CODEWITHSUNDEEP
pythonlist
user34
user34

Reputation: 46

How to find the index of matching elements in a list using Python?

I have two lists:

l1 = [1, 46, 8, 9, 4, 76, 797, 342, 3, 5, 67, 42, 87]
l2 = [42, 34, 5, 78, 8, 9, 4]

I want to find out the index of l1 that have matches in l2.

Can anyone help me out?

Upvotes: 0

Views: 79

Answers (2)

0Interest
0Interest

Reputation: 1842

The problem with enumerate and set is that it does not keep the order, here's a code that does this: 

print([l1.index(k) for k in l2 if k in l1])

Upvotes: 0

RMPR
RMPR

Reputation: 3531

Naive method:

for i in range(len(l1)):
    try:
        if l1[i] in l2:
            print(i)
    except ValueError:
        pass

You can also use a oneliner, which is more efficient because the lookup in a set is done in constant time, credits to @Matthias for pointing that out:

[i for i, v in enumerate(l1) if v in set(l2)]

Upvotes: 0

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