Counting distinct lists in a list

Question

I'm trying to remove the duplicate from the list and count the list after removing the duplicates

seq = [[1,2,3], [1,2,3], [2,3,4], [4,5,6]]
new_seq = [[1,2,3], [2,3,4], [4,5,6]]
count = 3 

My code takes around 23 seconds for around 66,000 lists in a list

How can I make my code faster?

def unique(seq):
 new_seq = []
 count = 0
 for i in seq:
 if i not in new_seq:
 new_seq.append(i)
 count += 1
 return count

• 200_success: What are you really trying to accomplish? Is this function part of a larger program? Tell us about the context.
• jack: The lists comes from another function which calculates an algorithm

Answer 1

Your function is slow because it is O(n²): each element being added to new_seq has to be compared against every previously added element.

To deduplicate a sequence, use a set. Constructing the set is only O(n) because it uses hashing.

Then, to obtain the size of the set, use len().

def unique(seq):
 return len(set(tuple(element) for element in seq))