Python – List Elements Grouping in Matrix

Given a Matrix, for groups according to list elements, i.e each group should contain all elements from List.

Input : test_list = [[2, 6], [7, 8], [1, 4]], check_list = [1, 2, 4, 6] 
Output : [[7, 8], [[1, 2], [4, 6]]] 
Explanation : 1, 2, 4, 6 elements rows are grouped. 

Input : test_list = [[2, 7], [7, 8], [1, 4]], check_list = [1, 2, 4, 6] 
Output : [[2, 7], [7, 8], [1, 4]] 
Explanation : No grouping possible.

Method : Using loop + list comprehension + Try-Except

In this, for each row in matrix, get elements missing from list, after getting elements, match with each row if we can find missing elements if found, the new group is made.

Python3

# Python3 code to demonstrate working of
# List Elements Grouping in Matrix
# Using loop

# initializing list
test_list = [[4, 6], [1, 2], [2, 6], [7, 8], [1, 4]]

# printing original list
print("The original list is : " + str(test_list))

# initializing check_list
check_list = [1, 2, 4, 6]


res = []
while test_list:

    # getting row
    sub1 = test_list.pop()

    # getting elements not in row
    sub2 = [ele for ele in check_list if ele not in sub1]
    try:

        # testing if we have list of removed elements
        test_list.remove(sub2)

        # grouping if present
        res.append([sub1, sub2])
    except ValueError:

        # ungrouped.
        res.append(sub1)

# printing result
print("The Grouped rows : " + str(res))

Output

The original list is : [[4, 6], [1, 2], [2, 6], [7, 8], [1, 4]]
The Grouped rows : [[[1, 4], [2, 6]], [7, 8], [[1, 2], [4, 6]]]

Time complexity: O(n^2), where n is the length of the input list test_list
Auxiliary space: O(n), where n is the length of the input list test_list.

Method 2: Looping over nested Loops in Python

1. Each row in the test_list
2. Here for each row, it creates a sublist called match to store the elements in the row that are in the check_list. 
3. It then loops over each element in the row, and if it finds an element that is not in the check_list, it breaks out of the loop and moves on to the next row.

Python3

test_list = [[4, 6], [1, 2], [2, 6], [7, 8], [1, 4]]
check_list = [1, 2, 4, 6]
res = []

# loop over each row in the test_list
for row in test_list:
    # create a sublist to store the matching elements
    match = []
    # loop over each element in the row
    for elem in row:
        # check if the element is in the check_list
        if elem in check_list:
            # if it is, add it to the match list
            match.append(elem)
        else:
            # if it's not, break out of the loop and move on to the next row
            break
    else:
        # if all elements in the row are in the check_list, append the row to the result
        res.append(row)
        continue
    # if we get to this point, some elements in the row are not in the check_list,
    # so we need to create a sublist to store those elements
    non_match = []
    for elem in row:
        if elem not in match:
            non_match.append(elem)
    # append both the match and non_match sublists to the result
    res.append([match, non_match])

print("The Grouped rows : " + str(res))

Output

The Grouped rows : [[4, 6], [1, 2], [2, 6], [[], [7, 8]], [1, 4]]

Time complexity: O(n*m), where n is the number of rows in the test_list and m is the maximum number of elements in any row. 
Auxiliary space: O(n*m), because we create a new list to store the result, and for each row that has elements that are not in the check_list, we create two new sublists to store the matching and non-matching elements.

Method 3: Using dictionary

You can use a dictionary to group the elements in the given list based on their value. Here’s how you can do it:

Python3

test_list = [[4, 6], [1, 2], [2, 6], [7, 8], [1, 4]]
check_list = [1, 2, 4, 6]

# initialize a dictionary with keys from check_list and empty lists as values
grouped_dict = {key: [] for key in check_list}

# iterate through each sublist in test_list
for sublist in test_list:
    # iterate through each element in the sublist
    for element in sublist:
        # check if the element is in the check_list
        if element in check_list:
            # append the sublist to the corresponding key in the dictionary
            grouped_dict[element].append(sublist)

# convert the dictionary to a list of sublists
grouped_list = [[grouped_dict[key], [key]] for key in check_list]

# print the result
print("The Grouped rows : " + str(grouped_list))

Output

The Grouped rows : [[[[1, 2], [1, 4]], [1]], [[[1, 2], [2, 6]], [2]], [[[4, 6], [1, 4]], [4]], [[[4, 6], [2, 6]], [6]]]

Time complexity: O(nm), where n is the length of the test_list and m is the length of the check_list. 
Auxiliary space: O(m + k), where m is the length of the check_list and k is the number of unique elements in test_list that are in check_list.

Method 4: Using set intersection

We can use set intersection to filter the test_list by the values in check_list and group them accordingly.

Approach:

1. Define test_list as a list of lists, where each sublist contains two integers.
2. Define check_list as a list of integers.
3. Create an empty list grouped_list to store the result.
4. Iterate through each value val in check_list.
5. Create an empty list sublists to store the sublists in test_list that contain the current value val.
6. Iterate through each sublist sublist in test_list.
7. Check if the current value val is in the sublist sublist.
8. If val is in sublist, append sublist to sublists.
9. Append sublists and val as a list to grouped_list.
10. Print the resulting list of lists.

Python3

test_list = [[4, 6], [1, 2], [2, 6], [7, 8], [1, 4]]
check_list = [1, 2, 4, 6]

grouped_list = []

# iterate through each value in check_list
for val in check_list:
    # create an empty list to store the sublists that contain the current value
    sublists = []
    # iterate through each sublist in test_list
    for sublist in test_list:
        # check if the current value is in the sublist
        if val in sublist:
            # append the sublist to the list of sublists
            sublists.append(sublist)
    # append the list of sublists and the current value to grouped_list
    grouped_list.append([sublists, [val]])

# print the result
print("The Grouped rows : " + str(grouped_list))

Output

The Grouped rows : [[[[1, 2], [1, 4]], [1]], [[[1, 2], [2, 6]], [2]], [[[4, 6], [1, 4]], [4]], [[[4, 6], [2, 6]], [6]]]

Time complexity: O(n*m), where n is the length of check_list and m is the length of the longest sublist in test_list. 
Auxiliary space: O(nm), where n is the length of check_list and m is the length of the longest sublist in test_list.

Method 5: Using a nested loop and a flag variable to keep track of grouped elements

This method iterates through each row in the list and then iterates through each element in the row. If an element is in the check_list, it is added to a grouped_row list. If an element is not in the check_list, it is added to an ungrouped_row list. At the end of the iteration through each element, if there are any ungrouped elements, they are added to the grouped_list. If there are any grouped elements, they are also added to the grouped_list. This method uses a flag variable to keep track of whether any grouped elements or ungrouped elements were found in the current row.

Python3

test_list = [[4, 6], [1, 2], [2, 6], [7, 8], [1, 4]]
check_list = [1, 2, 4, 6]
grouped_list = []

for row in test_list:
    grouped_row = []
    ungrouped_row = []
    for elem in row:
        if elem in check_list:
            grouped_row.append(elem)
        else:
            ungrouped_row.append(elem)
    if ungrouped_row:
        grouped_list.append(ungrouped_row)
    if grouped_row:
        grouped_list.append(grouped_row)

print("The Grouped rows : " + str(grouped_list))

Output

The Grouped rows : [[4, 6], [1, 2], [2, 6], [7, 8], [1, 4]]

Time complexity: O(n^2), where n is the total number of elements in the test_list.
Auxiliary space: O(n^2), since we are creating new lists for each grouped and ungrouped row, and appending these lists to the grouped_list. 

Method 6: Using the built-in function filter() along with lambda function.

Step-by-step approach:

• Define the test_list and check_list:
• Use the filter() function with a lambda function to select the elements in each row that are in the check_list:
• Combine the grouped and ungrouped elements for each row into a single list using a list comprehension:
• Print the grouped_list

Below is the implementation of the above approach:

Python3

test_list = [[4, 6], [1, 2], [2, 6], [7, 8], [1, 4]]
check_list = [1, 2, 4, 6]

grouped_rows = list(map(lambda row: list(filter(lambda x: x in check_list, row)), test_list))
ungrouped_rows = list(map(lambda row: list(filter(lambda x: x not in check_list, row)), test_list))

grouped_list = [row for row in grouped_rows + ungrouped_rows if row]

print("The Grouped rows : " + str(grouped_list))

Output

The Grouped rows : [[4, 6], [1, 2], [2, 6], [1, 4], [7, 8]]

Time complexity: O(n^2), where n is the number of rows in the test_list.
Auxiliary space: O(n^2), because two separate lists (grouped_rows and ungrouped_rows) are created to hold the filtered elements for each row in the test_list.