Collections¶
collections.Counter: Count the Occurrences of Items in a List¶
Counting the occurrences of each item in a list using a for-loop is slow and inefficient.
char_list = ['a', 'b', 'c', 'a', 'd', 'b', 'b']
def custom_counter(list_: list):
char_counter = {}
for char in list_:
if char not in char_counter:
char_counter[char] = 1
else:
char_counter[char] += 1
return char_counter
custom_counter(char_list)
{'a': 2, 'b': 3, 'c': 1, 'd': 1}
Using collections.Counter is more efficient, and all it takes is one line of code!
from collections import Counter
Counter(char_list)
Counter({'a': 2, 'b': 3, 'c': 1, 'd': 1})
In my experiment, using Counter is more than 2 times faster than using custom counter.
from timeit import timeit
import random
random.seed(0)
num_list = [random.randint(0,22) for _ in range(1000)]
numExp = 100
custom_time = timeit("custom_counter(num_list)", globals=globals())
counter_time = timeit("Counter(num_list)", globals=globals())
print(custom_time/counter_time)
2.6199148843686806