How to Concatenate dictionary value lists in Python

Concatenation is the process of combining two or more strings, lists, or other sequences into a single entity. It involves joining the elements of the sequences in a specific order to create a new sequence or string.

In Python, concatenation can be performed on various types of sequences, including strings, lists, tuples, and more. The specific method or operator used for concatenation depends on the type of sequences being combined.

Let's explore different approaches to concatenation in Python −

String Concatenation

When concatenating strings, the '+' operator or the str.join() method is commonly used. In the below example, the strings are concatenated with a space between them, resulting in the string "Hello World".

Example

# Using the `+` operator
string1 = "Hello"
string2 = "World"
concatenated_string = string1 + " " + string2
print("concatenation with +:",concatenated_string)
# Using `str.join()`:
strings = ["Hello", "World"]
concatenated_string = " ".join(strings)
print("concatenation with join():",concatenated_string)

Output

Following is the output of the above program −

concatenation with +: Hello World
concatenation with join(): Hello World

List Concatenation

To concatenate lists, the '+' operator or the extend() method can be used. Both approaches result in a new list that contains the elements of both lists combined.

Example

# Using the `+` operator
list1 = [1, 2, 3]
list2 = [4, 5, 6]
concatenated_list = list1 + list2
print("concatenation with +",concatenated_list)
# Using the `extend()` method
list1 = [1, 2, 3]
list2 = [4, 5, 6]
list1.extend(list2)
concatenated_list = list1
print("concatenation with extend():",concatenated_list)

Output

Following is the output of the above program −

concatenation with + [1, 2, 3, 4, 5, 6]
concatenation with extend(): [1, 2, 3, 4, 5, 6]

Tuple Concatenation

Concatenating tuples involves using the `+` operator. The `+` operator combines the elements of both tuples into a new tuple.

Example

# Using the `+` operator
tuple1 = (1, 2, 3)
tuple2 = (4, 5, 6)
concatenated_tuple = tuple1 + tuple2
print("concatenation with +:",concatenated_tuple)

Output

Following is the output of the above program −

concatenation with +: (1, 2, 3, 4, 5, 6)

Other Sequence Types

The concatenation techniques described above can be applied to other sequence types, such as sets and custom sequence classes, with some modifications based on their specific behaviors and requirements.

To concatenate the value lists of dictionaries in Python, we can use different approaches based on our specific requirements. Let’s see the each approach with an example in detail.

Using Loops

This approach assumes we have a dictionary where each key corresponds to a list of values, and we want to concatenate these lists into a single list.

Example

In this example, the `concatenate_dict_values()` function takes a dictionary i.e.`dictionary` as input. It initializes an empty list `result` to store the concatenated values. It then iterates through the values of the dictionary using a loop. For each and every iteration, it extends the `result` list with the values of the current key.

def concatenate_dict_values(dictionary):
   result = []
   for values in dictionary.values():
      result.extend(values)
   return result
dictionary = {"a" : [12,345,56,35,55],
   "b" : [23,4,25,64,345,4565]}
print("The concatenation of the value lists of dictionary:",concatenate_dict_values(dictionary))

Output

The concatenation of the value lists of dictionary: [12, 345, 56, 35, 55, 23,
4, 25, 64, 345, 4565]

Using the Itertools.chain.from_iterable() Function

This approach utilizes list comprehension and the `itertools.chain.from_iterable()` function to concatenate the value lists.

Example

In this example, the `concatenate_dict_values()` function takes a dictionary `dictionary` as input. It uses list comprehension to iterate over the values of the dictionary and flatten them into a single list. The `itertools.chain.from_iterable()` function is used to concatenate the value lists into a single iterable, which is then converted to a list.

import itertools
def concatenate_dict_values(dictionary):
   result = list(itertools.chain.from_iterable(dictionary.values()))
   return result
dictionary = {"a" : [12,345,56,35,55],
   "b" : [23,4,25,64,345,45,65]}
print("The concatenation of the value lists of dictionary:",concatenate_dict_values(dictionary))

Output

The concatenation of the value lists of dictionary: [12, 345, 56, 35, 55, 23,
4, 25, 64, 345, 45, 65]