Python – 按元组列表中第二个元素的频率排序

给定元组列表，按元组第二个元素的频率排序。

Input : test_list = [(6, 5), (1, 7), (2, 5), (8, 7), (9, 8), (3, 7)]
Output : [(1, 7), (8, 7), (3, 7), (6, 5), (2, 5), (9, 8)]
Explanation : 7 occurs 3 times as 2nd element, hence all tuples with 7, are aligned first.

Input : test_list = [(1, 7), (8, 7), (9, 8), (3, 7)]
Output : [(1, 7), (8, 7), (3, 7), (9, 8)]
Explanation : 7 occurs 3 times as 2nd element, hence all tuples with 7, are aligned first.

方法 #1：使用 sorted() + loop + defaultdict() + lambda

在此，我们使用 defaultdict() 计算频率，并使用此结果作为参数传递给 lambda函数，以在此基础上使用 sorted() 执行排序。

Python3

# Python3 code to demonstrate working of 
# Sort by Frequency of second element in Tuple List
# Using sorted() + loop + defaultdict() + lambda
from collections import defaultdict
  
# initializing list
test_list = [(6, 5), (2, 7), (2, 5), (8, 7), (9, 8), (3, 7)]
  
# printing original list
print("The original list is : " + str(test_list))
  
# constructing mapping
freq_map = defaultdict(int)
for idx, val in test_list:
    freq_map[val] += 1
  
# performing sort of result 
res = sorted(test_list, key = lambda ele: freq_map[ele[1]], reverse = True)
  
# printing results
print("Sorted List of tuples : " + str(res))

输出

The original list is : [(6, 5), (2, 7), (2, 5), (8, 7), (9, 8), (3, 7)]
Sorted List of tuples : [(2, 7), (8, 7), (3, 7), (6, 5), (2, 5), (9, 8)]

方法 #2：使用 Counter() + lambda + sorted()

在此，频率计算的任务是使用 Counter() 完成的，其余功能与上述方法类似。

Python3

# Python3 code to demonstrate working of 
# Sort by Frequency of second element in Tuple List
# Using Counter() + lambda + sorted()
from collections import Counter
  
# initializing list
test_list = [(6, 5), (2, 7), (2, 5), (8, 7), (9, 8), (3, 7)]
  
# printing original list
print("The original list is : " + str(test_list))
  
# constructing mapping using Counter
freq_map = Counter(val for key, val in test_list)
  
# performing sort of result 
res = sorted(test_list, key = lambda ele: freq_map[ele[1]], reverse = True)
  
# printing results
print("Sorted List of tuples : " + str(res))

输出

The original list is : [(6, 5), (2, 7), (2, 5), (8, 7), (9, 8), (3, 7)]
Sorted List of tuples : [(2, 7), (8, 7), (3, 7), (6, 5), (2, 5), (9, 8)]