How to sort a python list, based on different indices?-CodePudding

For instance, we have a list of list. The list should be reverse sorted based on some index i, and if there is tie, they should be sorted in ascending or descending order based on the condition.

For eg:

The list is [['A', 2, 4.2], ['B', 4, 4.5], ['C', 2, 3.3], ['D', 2, 3.5]]

How to sort this so that the result is:

[['B', 4, 4.5], ['A', 2, 4.2], ['D', 2, 3.5], ['C', 2, 3.3]]
[['B', 4, 4.5], ['C', 2, 3.3], ['D', 2, 3.5], ['A', 2, 4.2]]

In first condition, i want them to be sorted in descending order based on index 1, and then again on descending order on index 2 if there is tie on index 1.

In second condition, i want them to be sorted in descending order based on index 1, and then in ascending order on index 2 if there is tie on index 1.

CodePudding user response：

What I can think of is what follows:

myList = [['A', 2, 4.2], ['B', 4, 4.5], ['C', 2, 3.3], ['D', 2, 3.5]]
print(sorted(myList, key= lambda x: (x[1], x[2]), reverse=True))
print(sorted(myList, key= lambda x: (x[1], -1*x[2]), reverse=True))

Output

[['B', 4, 4.5], ['A', 2, 4.2], ['D', 2, 3.5], ['C', 2, 3.3]]
[['B', 4, 4.5], ['C', 2, 3.3], ['D', 2, 3.5], ['A', 2, 4.2]]

Explnatation

sorted function takes two argument: an iterable which can be a list, set or anything that is iterable, and a key, which defines the pattern of sorting. In the key argument, I have defined a tuple ((x[1], x[2])) that indicates the order of sorting, if the element with index 1 is tie, the it goes to check index number 2. The second sorted function is same, but when it goes to element with index number 2, it check its negative value in order to sort them in a ascending order.