# Python – Values frequencies of key

• Last Updated : 04 May, 2020

Sometimes, while working with Python dictionary lists, one can have a problem in which we require to find the frequency of all the values occurring in a specific key in dictionary list. This can have application across many domains including web development. Let’s discuss certain ways in which this task can be performed.

Input : test_list = [{‘gfg’: }, {‘good’: [5, 78, 10], ‘gfg’: [5, 6, 7, 8]}]
Output : {8: 1, 1: 1, 5: 1, 6: 1, 7: 1}

Input : test_list = [{‘gfg’: [1, 5, 6, 7]}]
Output : {1: 1, 5: 1, 6: 1, 7: 1}

Method #1 : Using `Counter()` + list comprehension
The combination of above functionalities is used to solve this problem. In this, we perform the task of finding frequency using Counter() and computation is done using list comprehension.

 `# Python3 code to demonstrate working of ``# Values frequencies of key``# Using Counter() + list comprehension``from` `collections ``import` `Counter`` ` `# initializing list``test_list ``=` `[{``'gfg'` `: [``1``, ``5``, ``6``, ``7``], ``'is'` `: [``9``, ``6``, ``2``, ``10``]},``             ``{``'gfg'` `: [``5``, ``6``, ``7``, ``8``], ``'good'` `: [``5``, ``7``, ``10``]},``             ``{``'gfg'` `: [``7``, ``5``], ``'best'` `: [``5``, ``7``]}]`` ` `# printing original list``print``(``"The original list is : "` `+` `str``(test_list))`` ` `# frequency key ``freq_key ``=` `"gfg"`` ` `# Values frequencies of key``# Using Counter() + list comprehension``res ``=` `Counter([idx ``for` `val ``in` `test_list ``for` `idx ``in` `val[freq_key]])`` ` `# printing result ``print``(``"The frequency dictionary : "` `+` `str``(``dict``(res))) `

Output :

The original list is : [{‘gfg’: [1, 5, 6, 7], ‘is’: [9, 6, 2, 10]}, {‘gfg’: [5, 6, 7, 8], ‘good’: [5, 7, 10]}, {‘gfg’: [7, 5], ‘best’: [5, 7]}]

The frequency dictionary : {8: 1, 1: 1, 5: 3, 6: 2, 7: 3}

Method #2 : Using `chain.from_iterables() + Counter()`
The combination of above methods can be used to solve this problem. In this, we perform the task of iteration and binding using chain.from_iterables().

 `# Python3 code to demonstrate working of ``# Values frequencies of key``# Using chain.from_iterables() + Counter()``from` `collections ``import` `Counter``import` `itertools`` ` `# initializing list``test_list ``=` `[{``'gfg'` `: [``1``, ``5``, ``6``, ``7``], ``'is'` `: [``9``, ``6``, ``2``, ``10``]},``             ``{``'gfg'` `: [``5``, ``6``, ``7``, ``8``], ``'good'` `: [``5``, ``7``, ``10``]},``             ``{``'gfg'` `: [``7``, ``5``], ``'best'` `: [``5``, ``7``]}]`` ` `# printing original list``print``(``"The original list is : "` `+` `str``(test_list))`` ` `# frequency key ``freq_key ``=` `"gfg"`` ` `# Values frequencies of key``# Using chain.from_iterables() + Counter()``res ``=` `Counter(itertools.chain.from_iterable([sub[freq_key] ``for` `sub ``in` `test_list]))`` ` `# printing result ``print``(``"The frequency dictionary : "` `+` `str``(``dict``(res))) `

Output :

The original list is : [{‘gfg’: [1, 5, 6, 7], ‘is’: [9, 6, 2, 10]}, {‘gfg’: [5, 6, 7, 8], ‘good’: [5, 7, 10]}, {‘gfg’: [7, 5], ‘best’: [5, 7]}]

The frequency dictionary : {8: 1, 1: 1, 5: 3, 6: 2, 7: 3}

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