Is there a built in function for string natural sort?

by

There is a third party library for this on PyPI called natsort (full disclosure, I am the package’s author). For your case, you can do either of the following:

>>> from natsort import natsorted, ns
>>> x = ['Elm11', 'Elm12', 'Elm2', 'elm0', 'elm1', 'elm10', 'elm13', 'elm9']
>>> natsorted(x, key=lambda y: y.lower())
['elm0', 'elm1', 'Elm2', 'elm9', 'elm10', 'Elm11', 'Elm12', 'elm13']
>>> natsorted(x, alg=ns.IGNORECASE)  # or alg=ns.IC
['elm0', 'elm1', 'Elm2', 'elm9', 'elm10', 'Elm11', 'Elm12', 'elm13']

You should note that natsort uses a general algorithm so it should work for just about any input that you throw at it. If you want more details on why you might choose a library to do this rather than rolling your own function, check out the natsort documentation’s How It Works page, in particular the Special Cases Everywhere! section.

If you need a sorting key instead of a sorting function, use either of the below formulas.

>>> from natsort import natsort_keygen, ns
>>> l1 = ['elm0', 'elm1', 'Elm2', 'elm9', 'elm10', 'Elm11', 'Elm12', 'elm13']
>>> l2 = l1[:]
>>> natsort_key1 = natsort_keygen(key=lambda y: y.lower())
>>> l1.sort(key=natsort_key1)
>>> l1
['elm0', 'elm1', 'Elm2', 'elm9', 'elm10', 'Elm11', 'Elm12', 'elm13']
>>> natsort_key2 = natsort_keygen(alg=ns.IGNORECASE)
>>> l2.sort(key=natsort_key2)
>>> l2
['elm0', 'elm1', 'Elm2', 'elm9', 'elm10', 'Elm11', 'Elm12', 'elm13']

Update November 2020

Given that a popular request/question is “how to sort like Windows Explorer?” (or whatever is your operating system’s file system browser), as of natsort version 7.1.0 there is a function called os_sorted to do exactly this. On Windows, it will sort in the same order as Windows Explorer, and on other operating systems it should sort like whatever is the local file system browser.

>>> from natsort import os_sorted
>>> os_sorted(list_of_paths)
# your paths sorted like your file system browser

For those needing a sort key, you can use os_sort_keygen (or os_sort_key if you just need the defaults).

Caveat – Please read the API documentation for this function before you use to understand the limitations and how to get best results.

More Related Contents:

  1. How do I sort a dictionary by value?
  2. How to sort a list of objects based on an attribute of the objects?
  3. Sort a list by multiple attributes?
  4. how to sort pandas dataframe from one column
  5. Python list sort in descending order
  6. How to sort two lists (which reference each other) in the exact same way
  7. How to sort a list of lists by a specific index of the inner list?
  8. Combining two sorted lists in Python
  9. Custom Python list sorting
  10. heapq with custom compare predicate
  11. Natural sorting
  12. How can I “zip sort” parallel numpy arrays?
  13. Python Math – TypeError: ‘NoneType’ object is not subscriptable
  14. What is the complexity of the sorted() function?
  15. Sorting dictionary keys in python [duplicate]
  16. Why is the cmp parameter removed from sort/sorted in Python3.0?
  17. Making a python user-defined class sortable, hashable
  18. Sort invariant for numpy.argsort with multiple dimensions
  19. Given parallel lists, how can I sort one while permuting (rearranging) the other in the same way?
  20. Pandas DataFrame sort by categorical column but by specific class ordering
  21. Sort a list of tuples by second value, reverse=True and then by key, reverse=False
  22. Python sorting complexity on sorted list
  23. Can I sort text by its numeric value in Python?
  24. Sort list while pushing None values to the end
  25. What is the space complexity of the python sort?
  26. What arguments does Python sort() function have?
  27. How can I sort a list, according to where its elements appear in another list?
  28. Sort strings by the first N characters
  29. Multi Index Sorting in Pandas
  30. Sort array’s rows by another array in Python

Leave a Comment