Let us starting simple and start with easy sort. Python has two sort functions; one function that sorts a list in-place and the other sort function “sorted” that creates a new sorted list. In this post, we will see examples of “in-place” sorting.
Python’s in-place sorting
As the name suggests the in-place sorting replaces the original un-sorted list to a new sorted list. If you have a list named myList and want to sort it using in-place sorting,
just call the built-in method as myList.sort()
For example,
>myList = [66,11,88, 44, 77] >myList.sort() >myList [11, 44, 66, 77, 88]
Remember, myList can contain a numbers or strings. For example, if you are sorting strings, Python will sort it alphabatically as
>myList=['line', 'cmd', 'tips'] >myList.sort() >myList ['cmd', 'line', 'tips']
How to Sort a List Numerically?
Often you might have numbers as string and you might want to sort numerically. However, Python will do it alphabatically. For example, if you sort the list
>myList = ['50', '111', '1', '99', '10']
Python will do the sort alphabetically and give you
>myList.sort() >myList ['1', '10', '111', '50', '99']
If you really want to sort the string list by treating it as numeric, you can use the option “key” in Python sort function as
>myList = ['50', '111', '1', '99', '10'] >myList.sort(key=int) >myList ['1', '10', '50', '99', '111']
Often you will want to sort a list of strings based on some specific criteria in the string (a specific part of the string). One way to do is to use lambda function. For example a list with with numeric values as part of the string.
>myList =['cmd1','cmd10', 'cmd111', 'cmd50', 'cmd99']
Using myList.sort() will sort the list alphabatically.
>myList.sort() >myList ['cmd1', 'cmd10', 'cmd111', 'cmd50', 'cmd99']
How to Sort a List in Python using Lambda Functions?
Often, one may want to sort a list but based on part of the elements of the items in the list. For example, you want to sort a list of strings using the numerical part of the string.
We can use write custom functions or lambda functions to sort the list according the numeric value in each of string in the list. For example
>myList =['cmd1','cmd10', 'cmd111', 'cmd50', 'cmd99'] # sort numerically with lambda function >myList.sort(key=lambda x: int(x[3:])) >myList ['cmd1', 'cmd10', 'cmd50', 'cmd99', 'cmd111']
where the key is a lambda function that takes string as input and the numeric value as output.
Here is one more example of sorting lists using lambda function. Again we will be sorting a list of string based on part of string.
>myList = ['cmd_line1','cmd_line10.com', 'cmd_line111', 'cmd_line50', 'cmd_line99']
# sort numerically with lambda function
>myList.sort(key=lambda x: int(x.split('_')[1][4:]))
>myList
['cmd_line1', 'cmd_line10.com', 'cmd_line111', 'cmd_line50', 'cmd_line99']
