How do you combine two lists in a column in python?

Join Two Lists

There are several ways to join, or concatenate, two or more lists in Python.

One of the easiest ways are by using the + operator.

Example

Join two list:

list1 = ["a", "b" , "c"]
list2 = [1, 2, 3]

list3 = list1 + list2
print(list3)

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Another way to join two lists are by appending all the items from list2 into list1, one by one:

Example

Append list2 into list1:

list1 = ["a", "b" , "c"]
list2 = [1, 2, 3]

for x in list2:
  list1.append(x)

print(list1)

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Or you can use the extend() method, which purpose is to add elements from one list to another list:

Example

Use the extend() method to add list2 at the end of list1:

list1 = ["a", "b" , "c"]
list2 = [1, 2, 3]

list1.extend(list2)
print(list1)

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Recipe Objective

Dataframes are data-objects in R which are combination of vectors of same length. It is represented as a two-dimensional array or a table where columns represent variables of the dataset while rows are the observations in it. Unlike matrices, dataframes contains different datatypes.

Often dataframes are created by loading a dataset from existing storage like an excel file, csv file. But we can also create a dataframe from vectors or lists in R. This recipe demonstrates how to create a dataframe combining 2 lists.

Table of Contents

• Recipe Objective
  • Step 1: Creating 2 lists
  • Step 2: Creating a Dataframe

Step 1: Creating 2 lists

We are going to take an example of student dataset which has variables like marks and name. To create this dataframe, we will first create 2 lists named "marks" and "name".

Note: the length of each lists has to be same

name = list('Tom', "Harry", "David", "Daniel") marks = list(50,60,35,95)

Step 2: Creating a Dataframe

We use data.frame() and unlist() functions to create a dataframe using lists. unlist() function is used to covert list to vector so that we can use it as "df" argument in data.frame() function.

Syntax:

1. data.frame(df, stringAsFactors)

where:

1. df = is matrix or collection of vectors that needs to be joined;
2. stringAsFactors = if TRUE, it converts string to vector by default;

unlist(x, recursive = TRUE, use.names = TRUE)

where:

1. x = lists;
2. recursive = By defalut it's TRUE but if FALSE, the function won't recurse beyond first level of list;
3. use.names = By default it's TRUE and its meant to preserve the naming information;

student = data.frame(unlist(name),unlist(marks)) ​ #to name the columns we use names() function names(student) = c("Name","Marks") ​ ​ student

Tom	50
Harry	60
David	35
Daniel	95

You can use either of the following templates in order to concatenate two lists in Python:

(1) Using the + operator:

list_one = ['item1', 'item2', 'item3', ....]
list_two = ['item1', 'item2', 'item3', ....]

concatenated_list = list_one + list_two
print(concatenated_list)

(2) Using extend:

list_one = ['item1', 'item2', 'item3', ....]
list_two = ['item1', 'item2', 'item3', ....]

list_one.extend(list_two)
print(list_one)

In the next section, you’ll see how to apply the above techniques in practice.

Step 1: Create two Lists

To begin with a simple example, let’s create two lists that contain string values:

list_one = ['Banana', 'Apple', 'Mango', 'Watermelon', 'Pear']
list_two = ['Blueberry', 'Cherry', 'Pineapple', 'Papaya', 'Coconut']

print(list_one)
print(list_two)

Run the code in Python, and you’ll get these two lists:

['Banana', 'Apple', 'Mango', 'Watermelon', 'Pear']
['Blueberry', 'Cherry', 'Pineapple', 'Papaya', 'Coconut']

Step 2: Concatenate the two Python Lists using the + operator

You can use the + operator in order to concatenate the two lists:

list_one = ['item1', 'item2', 'item3', ....]
list_two = ['item1', 'item2', 'item3', ....]

concatenated_list = list_one + list_two
print(concatenated_list)

For our example:

list_one = ['Banana', 'Apple', 'Mango', 'Watermelon', 'Pear']
list_two = ['Blueberry', 'Cherry', 'Pineapple', 'Papaya', 'Coconut']

concatenated_list = list_one + list_two
print(concatenated_list)

As you can see, the two lists are now concatenated:

['Banana', 'Apple', 'Mango', 'Watermelon', 'Pear', 'Blueberry', 'Cherry', 'Pineapple', 'Papaya', 'Coconut']

Similarly, you can use the + operator to concatenate two lists that contain integers:

list_one = [1, 2, 3, 4, 5]
list_two = [6, 7, 8, 9, 10]

concatenated_list = list_one + list_two
print(concatenated_list)

Here is the result:

[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

Using Extend

Alternatively, you can use extend to concatenate the two lists:

list_one = ['item1', 'item2', 'item3', ....]
list_two = ['item1', 'item2', 'item3', ....]

list_one.extend(list_two)
print(list_one)

Here is the complete Python code for our example:

list_one = ['Banana', 'Apple', 'Mango', 'Watermelon', 'Pear']
list_two = ['Blueberry', 'Cherry', 'Pineapple', 'Papaya', 'Coconut']

list_one.extend(list_two)
print(list_one)

Result:

['Banana', 'Apple', 'Mango', 'Watermelon', 'Pear', 'Blueberry', 'Cherry', 'Pineapple', 'Papaya', 'Coconut']

Concatenate More Than Two Lists

You can use the + operator to concatenate multiple lists.

For example, let’s concatenate the following 4 lists:

list_one = ['Banana', 'Apple', 'Mango']
list_two = ['Watermelon', 'Pear']
list_three = ['Blueberry', 'Cherry']
list_four = ['Pineapple', 'Papaya', 'Coconut']

concatenated_list = list_one + list_two + list_three + list_four
print(concatenated_list)

Run the code, and you’ll get the following result:

['Banana', 'Apple', 'Mango', 'Watermelon', 'Pear', 'Blueberry', 'Cherry', 'Pineapple', 'Papaya', 'Coconut']

Finally, you can check the following guide to learn more about creating a list in Python.

How do you combine two lists in python?

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