What if I want to return the list of occurrence of the values in list1
as compared to list2
as below?
list1 = [1, 2, 3, 4, 5]
list2 = [5, 6, 7, 8, 9]
I expect to get 0 occurrence of 1, 0 occurrence of 2, 0 occurrence of 3, 0 occurrence of 4, and 1 occurrence of 5; to have a new list as below,
new_list = [1, 0, 0, 0, 0]
See below by implementation. What am I doing wrong?
from collections import Counter
list1 = [1, 2, 3, 4, 5]
list2 = [5, 6, 7, 8, 9]
def matchingStrings(list1, list2):
count_all=Counter(list1)
counts= {x: count_all[x] for x in list2 if x in list1 }
list_output=list(counts.values())
print(list_output)
return list_output
# Write your code here
if __name__ == '__main__':
matchingStrings(list1,list2)
Output
Expected output
[1, 0, 0, 0, 0]
CodePudding user response:
Directly pass a set of he needed values to the Counter
then iterate on the list1
to get their count or 0
def matchingStrings(list1, list2):
counts = Counter(list1)
return [counts.get(value, 0) for value in list2]
print(matchingStrings(list1, list2)) # [1, 0, 0, 0, 0]
Benchmark of Counter
vs list.count
from collections import Counter, defaultdict
from datetime import datetime
import numpy as np
def matchingStrings(list1, list2):
counts = Counter(list1)
return [counts.get(value, 0) for value in list2]
def matchingStrings2(list1, list2):
return [list1.count(a) for a in list2]
if __name__ == '__main__':
nb = 5000
times = defaultdict(list)
for i in range(10):
list1 = list(np.random.randint(0, 100, nb))
list2 = list(np.random.randint(0, 100, nb))
s = datetime.now()
x1 = matchingStrings(list1, list2)
times["counter"].append(datetime.now() - s)
s = datetime.now()
x2 = matchingStrings2(list1, list2)
times["list"].append(datetime.now() - s)
print(np.mean(times['list']) / np.mean(times['counter']))
for key, values in times.items():
print(f"{key:7s} => {np.mean(values)}")
Counter is about 500 times faster
481.512173128945
counter => 0:00:00.003327
list => 0:00:01.601991
CodePudding user response:
A small correction fixes that:
from collections import Counter
list1 = [1, 2, 3, 4, 5]
list2 = [5, 6, 7, 8, 9]
def matchingStrings(list1, list2):
count_all=Counter(list2)
counts= {x: count_all[x] for x in list1 }
list_output=list(counts.values())
print(list_output)
return list_output
# Write your code here
if __name__ == '__main__':
matchingStrings(list1,list2)
CodePudding user response:
Try using the count
method.
list1 = [1, 2, 3, 4, 5]
list2 = [5, 6, 7, 8, 9]
def matchingStrings(list1, list2):
new_list = [list1.count(a) for a in list2]
print(new_list)
return new_list
if __name__ == '__main__':
matchingStrings(list1,list2)
OUTPUT:
[1, 0, 0, 0, 0]