Python list sorting methods and Examples

Python list sorting methods and Examples

Sorts lists. Python provides two methods.

Method 1: use the List built-in function list. sort for sorting.

List. sort (func = None, key = None, reverse = False)

Python instance:

>>> list = [2,5,8,9,3] >>> list [2,5,8,9,3] >>> list.sort() >>> list [2, 3, 5, 8, 9]

Method 2. sort by sequence type function sorted (list) (starting from 2.4)

Python instance:

>>> list = [2,5,8,9,3] >>> list [2,5,8,9,3] >>> sorted(list) [2, 3, 5, 8, 9]

Differences between the two methods:

Sorted (list) returns an object that can be used as an expression. The original list remains unchanged, and a new sorted list object is generated.

List. sort () does not return objects and changes the original list.

Other sort instances:

Instance 1: forward sorting

>>>L = [2,3,1,4]>>>L.sort()>>>L>>>[1,2,3,4]

Instance 2: reverse sorting

>>>L = [2,3,1,4]>>>L.sort(reverse=True)>>>L>>>[4,3,2,1]

Instance 3: sort the second keyword

>>>L = [('b',6),('a',1),('c',3),('d',4)]>>>L.sort(lambda x,y:cmp(x[1],y[1])) >>>L>>>[('a', 1), ('c', 3), ('d', 4), ('b', 6)]

Example 4: sort the second keyword

>>>L = [('b',6),('a',1),('c',3),('d',4)]>>>L.sort(key=lambda x:x[1]) >>>L>>>[('a', 1), ('c', 3), ('d', 4), ('b', 6)]

Instance 5: sort the second keyword

>>>L = [('b',2),('a',1),('c',3),('d',4)]>>>import operator>>>L.sort(key=operator.itemgetter(1)) >>>L>>>[('a', 1), ('b', 2), ('c', 3), ('d', 4)]

Instance 6: (DSU method: Decorate-Sort-Undercorate)

>>>L = [('b',2),('a',1),('c',3),('d',4)]>>>A = [(x[1],i,x) for i,x in enumerate(L)] #i can confirm the stable sort>>>A.sort()>>>L = [s[2] for s in A]>>>L>>>[('a', 1), ('b', 2), ('c', 3), ('d', 4)]

In the preceding section, we use the List sorting method in Step 6. instance 3.4.5.6 can be used to sort an item in List item.

Sort the comparison keywords.

Efficiency Comparison:

Cmp <DSU <key

Through experimental comparison, method 3 is slower than Method 6, Method 6 is slower than method 4, and method 4 and Method 5 are basically equivalent.

Sort multiple keywords by comparison:

Instance 7:

>>>L = [('d',2),('a',4),('b',3),('c',2)]>>> L.sort(key=lambda x:x[1])>>> L>>>[('d', 2), ('c', 2), ('b', 3), ('a', 4)]

We can see that the sorted L is only sorted by the second keyword,

What if we want to sort by the second keyword and then sort by the first keyword? There are two methods

Instance 8:

>>> L = [('d',2),('a',4),('b',3),('c',2)]>>> L.sort(key=lambda x:(x[1],x[0]))>>> L>>>[('c', 2), ('d', 2), ('b', 3), ('a', 4)]

Instance 9:

>>> L = [('d',2),('a',4),('b',3),('c',2)]>>> L.sort(key=operator.itemgetter(1,0))>>> L>>>[('c', 2), ('d', 2), ('b', 3), ('a', 4)]

Why does instance 8 work? The reason is that tuple is compared from left to right, and the first is compared. If it is equal, the second is compared.

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