Removing dupes in list of lists in Python

user_10277071 0
Viewed 501

Basically, I'm trying to do remove any lists that begin with the same value. For example, two of the below begin with the number 1:

a = [[1,2],[1,0],[2,4],[3,5]]

Because the value 1 exists at the start of two of the lists -- I need to remove both so that the new list becomes:

b = [[2,4],[3,5]]

How can I do this?

I've tried the below, but the output is: [[1, 2], [2, 4], [3, 5]]

def unique_by_first_n(n, coll):
    seen = set()
    for item in coll:
        compare = tuple(item[:n])
        print compare   # Keep only the first `n` elements in the set
        if compare not in seen:
            seen.add(compare)
            yield item

a = [[1,2],[1,0],[2,4],[3,5]]

filtered_list = list(unique_by_first_n(1, a))
python-2.7 list python
4 Answers

An efficient solution would be to create a Counter object to hold the occurrences of the first elements, and then filter the sub-lists in the main list:

from collections import Counter
counts = Counter(l[0] for l in a)
filtered = [l for l in a if counts[l[0]] == 1]
#[[2, 4], [3, 5]]
user_74343650

If you are happy to use a 3rd party library, you can use Pandas:

import pandas as pd

a = [[1,2],[1,0],[2,4],[3,5]]

df = pd.DataFrame(a)
b = df.drop_duplicates(subset=[0], keep=False).values.tolist()

print(b)

[[2, 4], [3, 5]]

The trick is the keep=False argument, described in the docs for pd.DataFrame.drop_duplicates.

user_92095460

You can use collections.Counter with list comprehension to get sublists whose first item appears only once:

from collections import Counter
c = Counter(n for n, _ in a)
b = [[x, y] for x, y in a if c[x] == 1]
user_68909120

Solution 1

a = [[1,2],[1,0],[2,4],[3,5]]
b = []
for item in a:
    i = 0
    if item[0] == a[i][0]:
        i =+ 1
        continue
    else:
        b.append(item)
        i += 1

Solution 2

a = [[1,2],[1,0],[2,4],[3,5]]
b = []

for item in a:
    for i in range(0, len(a)):
        if item[0] == a[i][0]:
            break
        else:
            if item in b:
                continue
            else:
                b.append(item)

Output

(xenial)vash@localhost:~/pcc/10$ python3 remove_help.py 
[[1, 2], [1, 0], [2, 4], [3, 5]]
[[2, 4], [3, 5]]

Achieved your goal no complex methods involed! Enjoy!

user_102556520
Related