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Concatenate List in Python (6 Methods with Example)
- Nov 23, 2021
- 5 Minutes Read
- Why Trust Us We uphold a strict editorial policy that emphasizes factual accuracy, relevance, and impartiality. Our content is crafted by top technical writers with deep knowledge in the fields of computer science and data science, ensuring each piece is meticulously reviewed by a team of seasoned editors to guarantee compliance with the highest standards in educational content creation and publishing.
- By Shivali Bhadaniya
Python possesses a wide range of in-built data structures, which helps programmers to code effectively and quickly. Lists is one such data structure highly used compared to other data structures while programming in python. It is because the list provides a wide range of features, and it is easily compatible with storing massive data under a single variable. To learn more about lists data structure, visit our article " 5 Ways to Convert Set to List in Python ".
As lists are the programmer's first choice to work with, in this article, we will study how to concatenate lists in python externally using various methods. We will also refer to respective examples of each method for your clear understanding. So, let’s get started!
How to Concatenate a List in Python?
Concatenation is the process of combining elements of a particular data structure in an end-to-end manner . Here we are talking about list data structure, and hence, we will join the elements of one list to the end of another list. Below is the 6 method by which python concatenate lists:
1) Using concatenation operation
The most conventional method to concatenate lists in python is by using the concatenation operator(+) . The “+” operator can easily join the whole list behind another list and provide you with the new list as the final output as shown in the below example.
For example:
2) Naïve method
In this method, you have to traverse through the elements of the second list using for loop and then append those elements at the end of the first list. To append the elements, we can use the python in-built method append() as shown in the below example. As the elements are appended at the end of first lists, the program will return the first lists itself as the final output.
3) Using the list of comprehensive
List comprehension is the process of generating the list elements depending on the existing list . You can easily concatenate two lists in python using the list comprehensive technique. Here, you can make use of for loop to traverse through the list element and later concatenate it, as shown in the below example.
4) Using extend() method
Python provides the in-built function extend() which can help you to concatenate two lists together. This function helps you to perform the inplace extension of the first list by iterating over the passed parameter and joining the elements of the list in a linear fashion .
5) Using the ‘*’ operator
“*” operator in python helps to unpack the collection of items in any data structure. Using the “*” operator, you can concatenate any number of lists, and hence the new list is returned as output. Remember, this method is only used in python version 3.6+ .
6) Using itertools.chain() method
Python possesses a large range of library collections one of which is “itertools” . Itertools library possesses the in-built function “chain()” which helps python concatenate lists easily. The itertools.chain() method accepts various data structures and results into the linear sequence as the output.
Remember that the data type of the element does not affect the working of the chain() method. Also, you have to import the itertools library using the “import” keyword as shown in the below example:
As lists are primarily used data structure while programming, often you face the situation of combining two or more lists. In this article, we have presented 6 standard methods by which you can easily concatenate lists in python along with examples and output. It is highly recommended to learn and understand this method to make your programming efficient.
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Shivali Bhadaniya
More by favtutor blogs, reverse level order traversal in binary tree (with code), vedanti kshirsagar.
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Python List Concatenation: Best Practices
In Python programming, the most used data structure is a list. It allows us to manipulate and organize data elements efficiently. Lists are particularly useful in data analysis, machine learning, and game development. As a data analyst, we apply different functions using lists. From those concatenation is an important function that involves joining multiple lists into a single.
The process of combining two or more lists into a single unified list is called concatenation. The most common approach to concatenate a list is done by using the “+” operator that appends elements of one list to another.
In this blog, we will explore 9 different concatenation methods that empower data analysts and developers to handle a wide range of programming challenges.
What is a Python List?
Before exploring the concatenation methods, let’s first understand the concept of lists and learn how to create one in Python.
Lists are data structures in Python in which we can store elements with different data types. We can create a list in Python by putting elements inside square brackets as follows.
Nine Ways to Concatenate Lists in Python
The following are Nine ways to concatenate lists in Python. Let’s explore each of them one by one using examples.
- Using the “+” operator
- Using Naive Method
- Using list comprehension
- Using extend() method
- Using “*” operator
- Using itertools.chain()
- Merge two List using reduce() function
- Using “+=” Operator
- Using NumPy `concatenate()` Function
1. Concatenation Using “+” Operator
The most common method to concatenate lists is the use of the “+” operator. It appends the elements of one list at the end of another list. This method is useful only for a small number of lists and not much efficient with a large number of lists due to its memory usage.
Let’s see how we can join two lists using this method:
2. Concatenation Using Naive Method
In this method we use for loop to traverse the second list and the elements get appended to the first list. So that the first list would have all the elements.
For example, to merge two lists using the Naive method we will use the following code.
3. Concatenation Using List Comprehension
List concatenating in Python using the comprehension method is a concise way to create a list of elements based on an existing list. It is also used for loop to traverse the list.
We can create a list using the comprehension method by using the following lines of code.
In the above code, the outer loop is for the sub-list, and the inner loop is for elements in the sub-list.
4. Concatenating Using extend() Method
Concatenation can be done by using extend() method in Python. It modifies the original list by adding all the elements of a list to the end of other lists. The syntax to use extend() method is as follows.
The following code example shows the concatenation using extend() method in Python.
Concatenation through extend() method is better than using the “+” operator because it modifies the original list rather than creating a new list.
5. Concatenation Using “*” Operator
In Python asterisk “*” can be used to concatenate two or more lists. The “*” operator unpacks the elements of each list and spreads out them into a new list.
This method is useful to join multiple lists at once. For example, we can join three lists as follows.
6. Concatenation Using itertools.chain()
To concatenate lists we can use itertools.chain() function offered by itertools modules in Python. It is used to concatenate different iterable objects like lists, strings, tuples, and dictionaries in a memory-efficient way.
The following example shows concatenation using itertools.chain() function.
7. Concatenation Using reduce() Function
In python reduce() function from functools library can be used to concatenate lists but first, we need to import the library.
The following example shows how we can combine two lists using reduce() function.
In the above code example we:
- Initialize two variables that hold two different lists.
- Create another list to store all the lists taken in the previous step, forming a nested list.
- Use the reduce() function and pass the nested list as a parameter, along with two variables.
- Use the lambda function to perform the concatenation operation and store the result in a list.
8. Concatenation Using “+=” Operator
In Python, the augmented assignment (+=) can also be used to concatenate the list just like the extend() method. This operation changes the original list by adding the elements of another list to its end.
The following code shows the concatenation using this approach.
The augmented assignment (+=) operator is the best choice to make a new concatenated list when you don’t want to keep the original list because this method modifies the original list.
9. Concatenation Using NumPy concatenate() Function
Python’s NumPy library also offers concatenate() function to join two or more lists but as a result, it returns a NumPy array instead of a list.
The following code can be used to perform concatenation using this method.
We use this method mostly when we are working with numerical data. To use NumPy for concatenation first, we need to import the NumPy library using the following syntax.
In this article, we have learned the different methods of list concatenation and how we can perform these functions in Python. List concatenation is an important operation in Python and its understanding is necessary for any programmer. It allows us to combine, manipulate, and data transformation in multiple ways. As we know there are many methods of concatenation each has its own strengths and weaknesses in terms of efficiency in handling complex tasks. By mastering different techniques we can choose the best one according to our needs.
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