How to use custom functions to sort a list

Custom functions

If you want to have your elements sorted in a specific manner you can define your own comparison function , of the form compare(x,y), which returns a negative number when x < y, a positive number when x > y, and zero when x == y (according to your definition).

You can then supply this as a parameter to sort. The built-in function cmp provides the default behavior:

print cmp(3, 2) #  w w  w .j  av a  2 s  . co  m
print cmp(99, 100) 
print cmp(10, 10) 
numbers = [5, 2, 9, 7] 
numbers.sort(cmp) 
print numbers 

The code above generates the following result.

The sort method has two other optional arguments: key and reverse. If you want to use them, you normally specify them by name. The key argument is similar to the cmp argument: You supply a function and it's used in the sorting process.

x = ['java2s.com', 'java', 'ruby', 'C#', 'Python'] 
x.sort(key=len) 
print x 

The code above generates the following result.

The other keyword argument, reverse, is simply a truth value indicating whether the list should be sorted in reverse:

x = [4, 6, 2, 1, 7, 9] 
x.sort(reverse=True) 
print x 

The code above generates the following result.

The following code compares lower strings.

caseList = ['d', 'B', 'F', 'A', 'E', 'c']
# w w w  . j av  a2 s .  c  om

print caseList
caseList.sort()
print caseList
caseList.sort(key=str.lower)
print caseList

The code above generates the following result.