Python – Group first elements by second elements in Tuple list
Given List of tuples, group 1st elements on basis of 2nd elements.
Input : test_list = [(6, 5), (2, 7), (2, 5), (8, 7), (3, 7)]
Output : {5: [6, 2], 7: [2, 8, 3]}
Explanation : 5 occurs along with 6 and 2 in tuple list, hence grouping.Input : test_list = [(6, 5), (2, 7), (2, 5), (8, 7)]
Output : {5: [6, 2], 7: [2, 8]}
Explanation : 5 occurs along with 6 and 2 in tuple list, hence grouping.
Method #1 : Using loop + groupby() + sorted() + list comprehension + lambda
In this, the elements are sorted for grouping, function provided by lambda, then only first elements are extracted using list comprehension out of result. And final dictionary formation using loop.
Python3
# Python3 code to demonstrate working of # Group first elements by second elements in Tuple list# Using loop + groupby() + sorted() + list comprehension + lambdafrom itertools import groupby # initializing listtest_list = [(6, 5), (2, 7), (2, 5), (8, 7), (9, 8), (3, 7)] # printing original listprint("The original list is : " + str(test_list)) res = dict() # forming equal groupsfor key, val in groupby(sorted(test_list, key = lambda ele: ele[1]), key = lambda ele: ele[1]): res[key] = [ele[0] for ele in val] # printing resultsprint("Grouped Dictionary : " + str(res)) |
The original list is : [(6, 5), (2, 7), (2, 5), (8, 7), (9, 8), (3, 7)]
Grouped Dictionary : {5: [6, 2], 7: [2, 8, 3], 8: [9]}
Method #2 : Using dictionary comprehension
This is method similar to above, just a one-liner shorthand handled using dictionary comprehension.
Python3
# Python3 code to demonstrate working of # Group first elements by second elements in Tuple list# Using dictionary comprehension from itertools import groupby # initializing listtest_list = [(6, 5), (2, 7), (2, 5), (8, 7), (9, 8), (3, 7)] # printing original listprint("The original list is : " + str(test_list)) # shorthand to solve problemres = {key : [v[0] for v in val] for key, val in groupby(sorted(test_list, key = lambda ele: ele[1]), key = lambda ele: ele[1])} # printing resultsprint("Grouped Dictionary : " + str(res)) |
The original list is : [(6, 5), (2, 7), (2, 5), (8, 7), (9, 8), (3, 7)]
Grouped Dictionary : {5: [6, 2], 7: [2, 8, 3], 8: [9]}
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