根据条件删除列表的元素

Question

I have a list of elements from which I want to remove those elements whose count is less than or equal to 2 in all the list.

For example:

A = [['a','b','c'],['b','d'],['c','d','e'],['c','e','f'],['b','c','e','g']]

I want to remove 'a' , 'd' , 'f' , 'g' from A and store the rest in B so that the list becomes:

B = [['b','c'],['b'],['c','e'],['c','e'],['b','c','e']]

I created a dictionary which will store all the count of elements and based on that I want to remove the elements with count less than or equal to 2.

Below is the code which I have written so far.

for i in range(len(A)):
    for words in A[i]:
        word_count[words] +=1
    B = [A[i] for i in range(len(A)) if word_count[words]<2]

Answer 1

You can use collections.Counter :

from collections import Counter
import itertools
A = [['a','b','c'],['b','d'],['c','d','e'],['c','e','f'],['b','c','e','g']]
c = Counter(itertools.chain(*A))
new_a = [[b for b in i if c[b] > 2] for i in A]

Output:

[['b', 'c'], ['b'], ['c', 'e'], ['c', 'e'], ['b', 'c', 'e']]

Answer 2

Before you add a new key to the dictionary , you have to check if the key exists . If not, just add the key to the dictionary . Otherwise, update the key's value.

A = [['a','b','c'],['b','d'],['c','d','e'],['c','e','f'],['b','c','e','g']]
word_count = {}
for i in range(len(A)):
  for words in A[i]:
    if words not in word_count:
      word_count[words] = 0
    word_count[words] += 1

Then filter the initial list using the created dictionary.

B = [[x for x in A[i] if word_count[x] > 2] for i in range(len(A))]
print(B)

Output

[['b', 'c'], ['b'], ['c', 'e'], ['c', 'e'], ['b', 'c', 'e']]