Reindex & Reset Index of pandas DataFrame from 0 in Python (3 Examples)

 

This tutorial shows how to reset and reindex the indices of a pandas DataFrame in the Python programming language.

Table of contents:

Let’s dive right in!

 

Example Data & Libraries

We first need to import the pandas library, if we want to use the corresponding functions:

import pandas as pd                          # Import pandas

Let’s also define some exemplifying data in Python:

data = pd.DataFrame({'x1':range(10, 18),     # Create pandas DataFrame
                     'x2':['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h'],
                     'x3':range(8, 0, - 1)},
                    index = [5, 6, 2, 1, 4, 7, 0, 3])
print(data)                                  # Print pandas DataFrame

 

table 1 DataFrame reindex pandas dataframe python

 

The previous table visualizes that our example pandas DataFrame has eight rows and three columns. The indices of this DataFrame are not ordered.

 

Example 1: Reindex pandas DataFrame Using reindex() Function

In this section, I’ll illustrate how to change the ordering of the indices of a pandas DataFrame in Python.

For this task, we first have to create a list that specifies the new order of our data set. Note that the values in this list are the same as the current index values:

new_index = [1, 6, 2, 7, 0, 3, 5, 4]         # Create list for new index
print(new_index)                             # Print new index
# [1, 6, 2, 7, 0, 3, 5, 4]

Next, we can sort the rows of our pandas DataFrame according to this list using the reindex function:

data_new1 = data.reindex(new_index)          # Apply reindex function
print(data_new1)                             # Print updated DataFrame

 

table 2 DataFrame reindex pandas dataframe python

 

As shown in Table 2, we have created a new pandas DataFrame by running the previous syntax. As you can see, the rows of this DataFrame have been rearranged according to the ordering in our list object.

 

Example 2: Reset Index of pandas DataFrame from 0 Using reset_index() Function

In Example 2, I’ll show how to reset the index numbers of a pandas DataFrame from 0 to the number of rows of the DataFrame.

To achieve this, we can apply the reset_index function as illustrated in the Python syntax below.

Within the reset_index function, we are also specifying the drop argument to be equal to True. This is an optional step. If we avoid this argument, a new column containing the original index will be added to the output.

Anyway, let’s do this in practice:

data_new2 = data.reset_index(drop = True)    # Apply reset_index function
print(data_new2)                             # Print updated DataFrame

 

table 3 DataFrame reindex pandas dataframe python

 

In Table 3 you can see that we have constructed a new pandas DataFrame with indices ranging consecutively from 0 to the number of rows of our data set.

Note that the values in the rows of this new data set have not been reordered, i.e. each row has a new index.

It is also possible to rearrange the values in a pandas DataFrame together with the indices, and this is what I will show you in the next example!

 

Example 3: Sort Rows of pandas DataFrame by Index Using sort_index() Function

This example shows how to order the rows of a pandas DataFrame by its index.

For this, we can use the sort_index function as shown below:

data_new3 = data.sort_index()                # Apply sort_sindex function
print(data_new3)                             # Print updated DataFrame

 

table 4 DataFrame reindex pandas dataframe python

 

As shown in Table 4, we have created another pandas DataFrame where the rows have been reordered according to the index numbers.

 

Video, Further Resources & Summary

I have recently released a video on my YouTube channel, which shows the Python programming codes of this article. You can find the video below.

 

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In addition, you could have a look at the related articles on this website. Some articles are listed below:

 

On this page you have learned how to reset, drop, and change the index of a pandas DataFrame in the Python programming language. In case you have any further comments or questions, don’t hesitate to let me know in the comments section.

 

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