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Python – Sort Matrix by Number of elements greater than its previous element

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  • Last Updated : 09 Aug, 2021
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Given a Matrix, sort by occurrences where next element is greater than current. Compute the count of i < i + 1 in each list, sort each row by count of each of this condition in each row.

Input : test_list = [[4, 6, 2, 9, 10], [5, 3, 2, 5], [2, 4, 5, 6, 7, 7], [6, 3, 2]] 
Output : [[6, 3, 2], [5, 3, 2, 5], [4, 6, 2, 9, 10], [2, 4, 5, 6, 7, 7]] 
Explanation : for [4, 6, 2, 9, 10], the count is 3 as 6>=4, 9>=2 and 10>=9, similarly for [5, 3, 2, 5], [2, 4, 5, 6,  7, 7], [6, 3, 2] counts are 1,4 and 0 respectively. As, 0<1<3<4 so the order of rows is [6, 3, 2], [5, 3, 2, 5], [4, 6, 2, 9, 10], [2, 4, 5, 6, 7, 7]
 

Input : test_list = [[5, 3, 2, 5], [2, 4, 5, 6, 7, 7], [6, 3, 2]] 
Output : [[6, 3, 2], [5, 3, 2, 5], [2, 4, 5, 6, 7, 7]] 
Explanation : 0 < 1 < 4, is the greater next greater elements count. No next element is greater in 1st list. 
 

Method #1 : Using sort() + len() 

In this, we perform task of sorting using sort() and call external function as the key to solve problem of counting elements with next element greater. The size is computed using len().

Python3




# Python3 code to demonstrate working of
# Sort Matrix by Next Greater Frequency
# Using sort() + len()
 
 
# getting frequency of next greater
def get_greater_freq(row):
 
    # getting length
    return len([row[idx] for idx in range(0, len(row) - 1) if row[idx] < row[idx + 1]])
 
 
# initializing list
test_list = [[4, 6, 2, 9, 10], [5, 3, 2, 5], [2, 4, 5, 6, 7, 7], [6, 3, 2]]
 
# printing original list
print("The original list is : " + str(test_list))
 
# inplace sorting
test_list.sort(key=get_greater_freq)
 
# printing result
print("Sorted rows : " + str(test_list))

Output:

The original list is : [[4, 6, 2, 9, 10], [5, 3, 2, 5], [2, 4, 5, 6, 7, 7], [6, 3, 2]] 
Sorted rows : [[6, 3, 2], [5, 3, 2, 5], [4, 6, 2, 9, 10], [2, 4, 5, 6, 7, 7]] 
 

Method #2 : Using sorted() + len() + lambda

In this, we perform task of sorting using sorted(), lambda and len() are used for creating one-liner functionality to perform sorting o the basis of number of elements greater than their previous element.

Python3




# Python3 code to demonstrate working of
# Sort Matrix by Next Greater Frequency
# Using sorted() + len() + lambda
 
# initializing list
test_list = [[4, 6, 2, 9, 10], [5, 3, 2, 5], [2, 4, 5, 6, 7, 7], [6, 3, 2]]
 
# printing original list
print("The original list is : " + str(test_list))
 
# performing one-liner sorting
# avoiding external fnc. call
res = sorted(test_list, key=lambda row: len(
    [row[idx] for idx in range(0, len(row) - 1) if row[idx] < row[idx + 1]]))
 
# printing result
print("Sorted rows : " + str(res))

Output:

The original list is : [[4, 6, 2, 9, 10], [5, 3, 2, 5], [2, 4, 5, 6, 7, 7], [6, 3, 2]] 
Sorted rows : [[6, 3, 2], [5, 3, 2, 5], [4, 6, 2, 9, 10], [2, 4, 5, 6, 7, 7]] 
 


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