Pandas reindex Method

The reindex method in Pandas is used to change the index of a DataFrame. It provides a powerful way to rearrange the data, add missing indices, or change the order of existing indices. This guide covers the syntax, example, output, explanation, use cases, important points, and a summary of the Pandas reindex method.

Syntax

import pandas as pd

# Using reindex with a new index
df.reindex(index=new_index, columns=new_columns)

# Using reindex to align with another DataFrame
df.reindex_like(other_dataframe)

Example

import pandas as pd

# Creating a DataFrame
data = {'Name': ['Alice', 'Bob', 'Charlie'],
        'Age': [25, 30, 35],
        'City': ['New York', 'San Francisco', 'Los Angeles']}

df = pd.DataFrame(data)

# Reindexing the DataFrame with a new index
new_index = [2, 0, 1]
df_reindexed = df.reindex(index=new_index)

# Displaying the reindexed DataFrame
print(df_reindexed)

Output

    Name  Age           City
2 Charlie  35    Los Angeles
0  Alice   25       New York
1    Bob   30  San Francisco

Explanation

• In the example, the reindex method is used to change the order of rows in the DataFrame based on the provided new_index.
• The original index was [0, 1, 2], and after reindexing, it becomes [2, 0, 1].
• The resulting DataFrame reflects the changes in the order of rows based on the new index.

Use

• Change Index Order: Reindexing is useful when you want to change the order of the rows in a DataFrame.
• Add Missing Indices: It can also be used to add new indices that were not present in the original DataFrame.
• Alignment with Other DataFrames: The reindex_like method allows aligning the DataFrame with another DataFrame's indices and columns.

Important Points

• reindex returns a new DataFrame with the specified index and columns, and it does not modify the original DataFrame in place.
• When reindexing, missing values are introduced for indices or columns that are not present in the original DataFrame.

Summary

The reindex method in Pandas is a versatile tool for changing the index and column order of a DataFrame. Whether you need to rearrange the rows, add missing indices, or align with another DataFrame, the reindex method provides a flexible and efficient solution. Keep in mind that it returns a new DataFrame, and the original DataFrame remains unchanged.