Python – Minimum value pairing for dictionary keys

Given two lists, key and value, construct a dictionary, which chooses minimum values in case of similar key value pairing.

Input : test_list1 = [4, 7, 4, 8], test_list2 = [5, 7, 2, 9]
Output : {8: 9, 7: 7, 4: 2}
Explanation : For 4, there are 2 options, 5 and 2, 2 being smallest is paired.

Input : test_list1 = [4, 4, 4, 4], test_list2 = [3, 7, 2, 1]
Output : {4: 1}
Explanation : All elements are for 4, smallest being 1.

Method #1 : dict() + sorted() + zip() + lambda

The combination of above functions can be used to solve this problem. In this, we perform sorting using sorted(), zip() is used to map keys with values. The dict() is used to convert result back into dictionary.

Python3

# Python3 code to demonstrate working of
# Minimum value pairing for dictionary keys
# Using dict() + sorted() + zip() + lambda

# initializing lists
test_list1 = [4, 7, 4, 8, 7, 9]
test_list2 = [5, 7, 2, 9, 3, 4]

# printing original lists
print("The original list 1 : " + str(test_list1))
print("The original list 2 : " + str(test_list2))

# using zip() to bing key and value lists
# reverse sorting the list before assigning values
# so as minimum values get to end, and hence avoided from
# pairing
res = dict(sorted(zip(test_list1, test_list2), key = lambda ele: -ele[1]))

# printing result
print("The minimum paired dictionary : " + str(res))

Output

The original list 1 : [4, 7, 4, 8, 7, 9]
The original list 2 : [5, 7, 2, 9, 3, 4]
The minimum paired dictionary : {8: 9, 7: 3, 4: 2, 9: 4}

Method #2 : Using groupby() + itemgetter() + zip()

The combination of above functions provide yet another way to solve this problem. In this, the values grouping is done using groupby() and minimum element is extracted using itemgetter().

Python3

# Python3 code to demonstrate working of
# Minimum value pairing for dictionary keys
# Using groupby() + itemgetter() + zip()
from operator import itemgetter
from itertools import groupby

# initializing lists
test_list1 = [4, 7, 4, 8, 7, 9]
test_list2 = [5, 7, 2, 9, 3, 4]

# printing original lists
print("The original list 1 : " + str(test_list1))
print("The original list 2 : " + str(test_list2))

# using zip() to bind key and value lists
# groupby() to group similar value.
# 0th, first element is extracted to be smallest
# using itemgetter()
temp = sorted(zip(test_list1, test_list2))
res = {key: min(val for _, val in group)
      for key, group in groupby(sorted(temp), itemgetter(0))}

# printing result
print("The minimum paired dictionary : " + str(res))

Output

The original list 1 : [4, 7, 4, 8, 7, 9]
The original list 2 : [5, 7, 2, 9, 3, 4]
The minimum paired dictionary : {4: 2, 7: 3, 8: 9, 9: 4}