In this article, we will learn how to sort a list or dictionary using multiple keys in Python.
Sorting a list or dictionary can be easily done using the sort() method and sorted() function in Python.
However, if you want to sort a list or dictionary by multiple elements, let’s say two keys then the easiest way is to use the key parameter and tuple the keys that we want to sort.
Let’s see some examples of sorting by two keys in Python.
Sort list of dictionaries by multiple keys
To sort a list of dictionaries we can use the sort() method in Python.
Now to sort the list of objects by two keys:
- We have to use the
keyargument in sort() method and pass thelambdafunction.
Note: The
keyis an optional argument that is used to sort items by different criteria. It can take functions to determine the sorting of items.
- Next, pass the tuple of the keys that we want to sort by to the sorting lambda expression.
Let’s see an example to sort a list of employee dictionaries by two keys: name and salary using sort() function.
employee_list = [
{'name': 'Jack','salary':2000},
{'name': 'Danny','salary':1000},
{'name': 'Adam','salary':1500},
{'name': 'Bob','salary':1000},
]
employee_list.sort(key= lambda x: (x["salary"],x["name"]))
print(employee_list)Output:
[{'name': 'Bob', 'salary': 1000}, {'name': 'Danny', 'salary': 1000}, {'name': 'Adam', 'salary': 1500}, {'name': 'Jack', 'salary': 2000}]In the above example, we have sorted the list of employee dictionaries by two keys: first by salary and second by the name key.
Sort List of Tuples by two keys in Python
If you have a list of tuples and you want to sort the values using two keys in Python, then we can use the sort() method and use a lambda function with the tuple to sort.
So to sort a list of tuples by two keys:
- Use the
sort()method on the list. - Use the
keyparameter and pass the lambda function. - Now select the values in the tuple you want to sort by using its specific indices. Here we will sort by the first two elements, so the index are
k[0]andk[1].
tuple_list = [('a','c','b'),('b','c','a'),('a','b','d'),('c','a','b')]
tuple_list.sort(key=lambda k: (k[0],k[1]))
print(tuple_list)Output:
[('a', 'b', 'd'), ('a', 'c', 'b'), ('b', 'c', 'a'), ('c', 'a', 'b')]This way you can sort tuples by multiple elements in python.
Sort a dictionary by two keys in Python
To sort a dictionary by two keys we have to use the sorted() function and pass the lambda function to the key parameter.
emp_list = {'Jack':2000, 'Danny': 1000, 'Adam': 1500, 'Bob': 1000}
sorted_list = sorted(emp_list, key= lambda x: (emp_list[x],x))
print(sorted_list)Output:
['Bob', 'Danny', 'Adam', 'Jack']It has printed out the list based on the salary and the name keys.
If you want to print out the salary along with the name in the output, we have to print out the results in tuple.
We can use the items() method of the dictionary object that returns the (key, value) tuple pair.
emp_list = {'Jack':2000, 'Danny': 1000, 'Adam': 1500, 'Bob': 1000}
sorted_list = sorted(emp_list.items(), key= lambda x: (x[1],x[0]))
print(sorted_list)Output:
[('Bob', 1000), ('Danny', 1000), ('Adam', 1500), ('Jack', 2000)]Here, the emp_list.items() returns the tuple with the key and value.
Next, we sorted the dictionary using two keys: salary and name of the employee.
Conclusion:
Here, we have learned how to sort a list, dictionary, and tuple by multiple keys using the list’s sort() method and the sorted() function in python.
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