Python – Group Similar items to Dictionary Values List

Given a list of elements, perform grouping of similar elements, as different key-value list in dictionary.

Input : test_list = [4, 6, 6, 4, 2, 2, 4, 8, 5, 8]
Output : {4: [4, 4, 4], 6: [6, 6], 2: [2, 2], 8: [8, 8], 5: [5]}
Explanation : Similar items grouped together on occurrences.

Input : test_list = [7, 7, 7, 7]
Output : {7 : [7, 7, 7, 7]}
Explanation : Similar items grouped together on occurrences.

Method #1 : Using defaultdict() + loop

This is one of the ways in which this task can be performed. In this, we construct a defaultdict() with default list and keep appending similar values into similar list.

Python3

 `# Python3 code to demonstrate working of  ` `# Group Similar items to Dictionary Values List ` `# Using defaultdict + loop ` `from` `collections ``import` `defaultdict ` ` `  `# initializing list ` `test_list ``=` `[``4``, ``6``, ``6``, ``4``, ``2``, ``2``, ``4``, ``4``, ``8``, ``5``, ``8``] ` ` `  `# printing original list ` `print``(``"The original list : "` `+` `str``(test_list)) ` ` `  `# using defaultdict for default list  ` `res ``=` `defaultdict(``list``) ` `for` `ele ``in` `test_list: ` `     `  `    ``# appending Similar values ` `    ``res[ele].append(ele) ` ` `  `# printing result  ` `print``(``"Similar grouped dictionary : "` `+` `str``(``dict``(res))) `

Output

```The original list : [4, 6, 6, 4, 2, 2, 4, 4, 8, 5, 8]
Similar grouped dictionary : {4: [4, 4, 4, 4], 6: [6, 6], 2: [2, 2], 8: [8, 8], 5: [5]}

```

Method #2 : Using dictionary comprehension + Counter()

This is yet another way in which this task can be performed. In this, we extract frequency using Counter() and then repeat occurrences using multiplication.

Python3

 `# Python3 code to demonstrate working of  ` `# Group Similar items to Dictionary Values List ` `# Using dictionary comprehension + Counter() ` `from` `collections ``import` `Counter ` ` `  `# initializing list ` `test_list ``=` `[``4``, ``6``, ``6``, ``4``, ``2``, ``2``, ``4``, ``4``, ``8``, ``5``, ``8``] ` ` `  `# printing original list ` `print``(``"The original list : "` `+` `str``(test_list)) ` ` `  `# using * operator to perform multiplication ` `res ``=` `{key : [key] ``*` `val ``for` `key, val ``in` `Counter(test_list).items()} ` ` `  `# printing result  ` `print``(``"Similar grouped dictionary : "` `+` `str``(res)) `

Output

```The original list : [4, 6, 6, 4, 2, 2, 4, 4, 8, 5, 8]
Similar grouped dictionary : {4: [4, 4, 4, 4], 6: [6, 6], 2: [2, 2], 8: [8, 8], 5: [5]}
```

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