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Python | Extract least frequency element
• Last Updated : 29 Nov, 2019

Sometimes, while working with data, we can have a problem in which we need to extract element which is occurring least number of times in the list. Let’s discuss certain ways in which this problem can be solved.

Method #1 : Using `defaultdict()` + loop
The combination of above functions can be used to perform this task. In this, we extract each element’s frequency using defaultdict() and extract the minimum frequency element after traversing the defaultdict.

 `# Python3 code to demonstrate working of``# Extract least frequency element``# using defaultdict() + loop``from` `collections ``import` `defaultdict`` ` `# initialize list ``test_list ``=` `[``1``, ``3``, ``4``, ``5``, ``1``, ``3``, ``5``]`` ` `# printing original list ``print``(``"The original list : "` `+` `str``(test_list))`` ` `# Extract least frequency element``# using defaultdict() + loop``res ``=` `defaultdict(``int``)``for` `ele ``in` `test_list:``   ``res[ele] ``+``=` `1` `min_occ ``=` `9999``for` `ele ``in` `res:``    ``if` `min_occ > res[ele]:``        ``min_occ ``=` `res[ele]``        ``tar_ele ``=` `ele`` ` `# printing result``print``(``"The minimum occurring element is : "` `+` `str``(tar_ele))`
Output :
```The original list : [1, 3, 4, 5, 1, 3, 5]
The minimum occurring element is : 4
```

Method #2 : Using `Counter()`
This method is similar to above, the difference is that the frequency is stored using Counter() and then we extract element with least frequency.

 `# Python3 code to demonstrate working of``# Extract least frequency element``# using Counter()``from` `collections ``import` `Counter`` ` `# initialize list ``test_list ``=` `[``1``, ``3``, ``4``, ``5``, ``1``, ``3``, ``5``]`` ` `# printing original list ``print``(``"The original list : "` `+` `str``(test_list))`` ` `# Extract least frequency element``# using Counter``res ``=` `Counter(test_list)``tar_ele ``=` `res.most_common()[``-``1``][``0``]`` ` `# printing result``print``(``"The minimum occurring element is : "` `+` `str``(tar_ele))`
Output :
```The original list : [1, 3, 4, 5, 1, 3, 5]
The minimum occurring element is : 4
```

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