# Python | Ways to Convert 3D List to 2D List

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Method # 1: Using ` defaultdict () ` + loop
A combination of the above functions can be used to accomplish this task. In this case, we extract the frequency of each element using defaultdict () and extract the minimum frequency element after passing the defaultdict.

 ` # Python3 demo code ` ` # Extract the lowest frequency element ` ` # using defaultdict () + loop ` ` from ` ` collections ` ` import ` ` defaultdict `   ` # initialize the list ` ` test_list ` ` = ` ` [` ` 1 , 3 , 4 , 5 , 1 , 3 , 5 ] ````   # print original list print ( "The original list:" + str (test_list))   # Retrieve the lowest 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 & gt; res [ele]: min_occ = res [ele] tar_ele = ele   # print 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 with Counter () and then we retrieve the element with n at the lowest frequency.

 ` # Python3 code to demonstrate how it works ` ` # Extract the lowest frequency element ` ` # using Counter () ` ` from ` ` collections ` ` import ` ` Counter `   ` # initialize the list ` ` test_list ` ` = ` ` [` ` 1 ` `, ` ` 3 ` `, ` ` 4 ` `, ` ` 5 ` `, ` ` 1 ` `, ` ` 3 , 5 ] ````   # print original list print ( "The original list:" + str (test_list))    # Retrieve the lowest frequency element # using counter res = Counter (test_list) tar_ele = res.most_common () [ - 1 ] [ 0 ]    # print 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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