Python: How to sort a list of dictionaries by several values?

by 
>>> A = [{'name':'john','age':45},
     {'name':'andi','age':23},
     {'name':'john','age':22},
     {'name':'paul','age':35},
     {'name':'john','age':21}]
>>> sorted(A, key = lambda user: (user['name'], user['age']))
[{'age': 23, 'name': 'andi'}, {'age': 21, 'name': 'john'}, {'age': 22, 'name': 'john'}, {'age': 45, 'name': 'john'}, {'age': 35, 'name': 'paul'}]

This sorts by a tuple of the two attributes, the following is equivalent and much faster/cleaner:

>>> from operator import itemgetter
>>> sorted(A, key=itemgetter('name', 'age'))
[{'age': 23, 'name': 'andi'}, {'age': 21, 'name': 'john'}, {'age': 22, 'name': 'john'}, {'age': 45, 'name': 'john'}, {'age': 35, 'name': 'paul'}]

From the comments: @Bakuriu

I bet there is not a big difference between the two, but itemgetter avoids a bit of overhead because it extracts the keys and make the tuple during a single opcode(CALL_FUNCTION), while calling the lambda will have to call the function, load the various constants(which are other bytecodes) finally call the subscript (BINARY_SUBSCR), build the tuple and return it… that’s a lot more work for the interpreter.

To summarize: itemgetter keeps the execution fully on the C level, so it’s as fast as possible.

More Related Contents:

  1. How do I sort a list of dictionaries by a value of the dictionary?
  2. Why does “return list.sort()” return None, not the list?
  3. Sorting list based on values from another list
  4. From list of integers, get number closest to a given value
  5. Pythonic way to check if a list is sorted or not
  6. sort() and reverse() functions do not work
  7. Finding median of list in Python
  8. Sorting Python list based on the length of the string
  9. How to sort and remove duplicates from Python list? [duplicate]
  10. case-insensitive list sorting, without lowercasing the result?
  11. List sorting with multiple attributes and mixed order
  12. Sorting a dictionary with lists as values, according to an element from the list
  13. Sort multidimensional array based on 2nd element of the subarray
  14. Python – How to sort a list of lists by the fourth element in each list? [duplicate]
  15. Sort a list of lists with a custom compare function
  16. django – convert a list back to a queryset [duplicate]
  17. Python data structure sort list alphabetically
  18. Sort list of strings by a part of the string
  19. Efficient method to calculate the rank vector of a list in Python
  20. Python .sort() not working as expected
  21. How to sort a list of objects based on an attribute of the objects in descending order?
  22. How do I sort a list of objects based on an attribute of the objects?
  23. Sorting list according to corresponding values from a parallel list [duplicate]
  24. How to sort multidimensional array by column?
  25. How to sort a 2D list? [closed]
  26. How to sort a list of strings in reverse order without using reverse=True parameter?
  27. Retrieve the two highest item from a list containing 100,000 integers
  28. Nested lambda statements when sorting lists
  29. How to find the max number(s) in a list with tied numbers
  30. How to sort a list of dictionaries by a value of the dictionary in Python?

Leave a Comment