Getting index of item while processing a list using map in python

Question

While processing a list using map(), I want to access index of the item while inside lambda. How can I do that?

For example

ranked_users = ['jon','bob','jane','alice','chris'] user_details = map(lambda x: {'name':x, 'rank':?}, ranked_users) 

How can I get rank of each user in above example?

Answer 1

Use enumerate:

In [3]: user_details = [{'name':x, 'rank':i} for i,x in enumerate(ranked_users)]   In [4]: user_details Out[4]:  [{'name': 'jon', 'rank': 0},  {'name': 'bob', 'rank': 1},  {'name': 'jane', 'rank': 2},  {'name': 'alice', 'rank': 3},  {'name': 'chris', 'rank': 4}] 

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PS. My first answer was

user_details = map(lambda (i,x): {'name':x, 'rank':i}, enumerate(ranked_users)) 

I'd strongly recommend using a list comprehension or generator expression over map and lambda whenever possible. List comprehensions are more readable, and tend to be faster to boot.

Answer 2

Alternatively you could use a list comprehension rather than map() and lambda.

ranked_users = ['jon','bob','jane','alice','chris'] user_details = [{'name' : x, 'rank' : ranked_users.index(x)} for x in ranked_users] 

Output:

[{'name': 'jon', 'rank': 0}, {'name': 'bob', 'rank': 1}, {'name': 'jane', 'rank': 2}, {'name': 'alice', 'rank': 3}, {'name': 'chris', 'rank': 4}] 

List comprehensions are very powerful and are also faster than a combination of map and lambda.