CODEWITHSUNDEEP
pythonpython-3.x
jef
jef

Reputation: 4083

Extract unique list from nested list in Python

I want to extract unique data from nested list, see below. I implemented two way of this. First one works good, but second one failed. Is new_data is empty during calculation? And how do I fix it?

 data = [                                                                                                                                      
     ['a', 'b'],                                                                                                                               
     ['a', 'c'],                                                                                                                               
     ['a', 'b'],                                                                                                                               
     ['b', 'a']                                                                                                                                
 ]                                                                                                                                             

 # working                                                                                                                                          
 new_data = []                                                                                                                                 
 for d in data:                                                                                                                                
     if d not in new_data:                                                                                                                     
         new_data.append(d)                                                                                                                    
 print(new_data)                                                                                                                               
 # [['a', 'b'], ['a','c'], ['b','a']]                                                                                                          

 # Failed to extract unique list                                                                                                                                 
 new_data = []                                                                                                                                 
 new_data = [d for d in data if d not in new_data]                                                                                             
 print(new_data)                                                                                                                               
 # [['a', 'b'], ['a', 'c'], ['a', 'b'], ['b', 'a']]

Upvotes: 1

Views: 6303

Answers (2)

Aaron
Aaron

Reputation: 11075

you could use enumerate to test that there are no copies before the current value such that only the first instance of a copy is taken:

new_data = [item for index, item in enumerate(data) if item not in data[:index]]

Upvotes: 0

Spencer Bard
Spencer Bard

Reputation: 1035

Just try:

new_data = [list(y) for y in set([tuple(x) for x in data])]

You cannot use set() on a list of lists because lists are not hashable. You convert the list of lists into a list of tuples. Apply set() to remove the duplicates. Then convert the de duplicated list of tuples back into a list of lists.

Upvotes: 5

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