search
HomeBackend DevelopmentPython TutorialHow to Efficiently Extract Rows from One Pandas DataFrame that are Absent in Another?

How to Efficiently Extract Rows from One Pandas DataFrame that are Absent in Another?

Retrieving Rows from One Dataframe that are Excluded from Another

In pandas, it is common to have multiple dataframes with potentially overlapping data. One task that frequently arises is isolating rows from one dataframe that are not present in another. This operation is particularly useful when working with subsets or filtering data.

Problem Formulation:

Given two pandas dataframes, where df1 contains a superset of rows compared to df2, we aim to obtain the rows in df1 that are not found in df2. The example below illustrates this scenario with a simple case:

import pandas as pd

df1 = pd.DataFrame(data={'col1': [1, 2, 3, 4, 5], 'col2': [10, 11, 12, 13, 14]})
df2 = pd.DataFrame(data={'col1': [1, 2, 3], 'col2': [10, 11, 12]})

print(df1)
print(df2)

# Expected result:
#   col1  col2
# 3     4    13
# 4     5    14

Solution:

To effectively address this problem, we employ a technique known as a left join. This operation merges df1 and df2 while ensuring that all rows from df1 are retained. Additionally, we include an indicator column to identify the origin of each row after the merge. By leveraging the unique rows from df2 and excluding duplicates, we achieve the desired result.

The python code below implements this solution:

df_all = df1.merge(df2.drop_duplicates(), on=['col1', 'col2'], how='left', indicator=True)
result = df_all[df_all['_merge'] == 'left_only']

Explanation:

  1. Left Join: The merge function performs a left join between df1 and df2.drop_duplicates(). This operation merges rows from df1 with rows from df2 based on the matching values in columns col1 and col2.
  2. Merge Indicator: The indicator parameter is set to True to include an extra column named _merge in the resulting dataframe df_all. This column indicates the origin of each row: 'both' for rows that exist in both df1 and df2, 'left_only' for rows exclusive to df1, and 'right_only' for rows exclusive to df2.
  3. Filter by 'left_only': To isolate rows from df1 that are not in df2, we filter the df_all dataframe by checking rows with _merge equal to 'left_only'. This gives us the desired result.

Avoiding Common Pitfalls:

It is important to note that some solutions may incorrectly check for individual column values instead of matching rows as a whole. Such approaches may lead to incorrect results, as illustrated in the example below:

~df1.col1.isin(common.col1) & ~df1.col2.isin(common.col2)

This code does not consider the joint occurrence of values in rows and may produce incorrect results when rows in df1 have values that appear individually in df2 but not in the same row.

By adopting the left join approach described above, we ensure that the derived rows are correctly identified as exclusive to df1. This technique provides a reliable and efficient solution to extracting rows that are present in one dataframe but not in another.

The above is the detailed content of How to Efficiently Extract Rows from One Pandas DataFrame that are Absent in Another?. For more information, please follow other related articles on the PHP Chinese website!

Statement
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn
Learning Python: Is 2 Hours of Daily Study Sufficient?Learning Python: Is 2 Hours of Daily Study Sufficient?Apr 18, 2025 am 12:22 AM

Is it enough to learn Python for two hours a day? It depends on your goals and learning methods. 1) Develop a clear learning plan, 2) Select appropriate learning resources and methods, 3) Practice and review and consolidate hands-on practice and review and consolidate, and you can gradually master the basic knowledge and advanced functions of Python during this period.

Python for Web Development: Key ApplicationsPython for Web Development: Key ApplicationsApr 18, 2025 am 12:20 AM

Key applications of Python in web development include the use of Django and Flask frameworks, API development, data analysis and visualization, machine learning and AI, and performance optimization. 1. Django and Flask framework: Django is suitable for rapid development of complex applications, and Flask is suitable for small or highly customized projects. 2. API development: Use Flask or DjangoRESTFramework to build RESTfulAPI. 3. Data analysis and visualization: Use Python to process data and display it through the web interface. 4. Machine Learning and AI: Python is used to build intelligent web applications. 5. Performance optimization: optimized through asynchronous programming, caching and code

Python vs. C  : Exploring Performance and EfficiencyPython vs. C : Exploring Performance and EfficiencyApr 18, 2025 am 12:20 AM

Python is better than C in development efficiency, but C is higher in execution performance. 1. Python's concise syntax and rich libraries improve development efficiency. 2.C's compilation-type characteristics and hardware control improve execution performance. When making a choice, you need to weigh the development speed and execution efficiency based on project needs.

Python in Action: Real-World ExamplesPython in Action: Real-World ExamplesApr 18, 2025 am 12:18 AM

Python's real-world applications include data analytics, web development, artificial intelligence and automation. 1) In data analysis, Python uses Pandas and Matplotlib to process and visualize data. 2) In web development, Django and Flask frameworks simplify the creation of web applications. 3) In the field of artificial intelligence, TensorFlow and PyTorch are used to build and train models. 4) In terms of automation, Python scripts can be used for tasks such as copying files.

Python's Main Uses: A Comprehensive OverviewPython's Main Uses: A Comprehensive OverviewApr 18, 2025 am 12:18 AM

Python is widely used in data science, web development and automation scripting fields. 1) In data science, Python simplifies data processing and analysis through libraries such as NumPy and Pandas. 2) In web development, the Django and Flask frameworks enable developers to quickly build applications. 3) In automated scripts, Python's simplicity and standard library make it ideal.

The Main Purpose of Python: Flexibility and Ease of UseThe Main Purpose of Python: Flexibility and Ease of UseApr 17, 2025 am 12:14 AM

Python's flexibility is reflected in multi-paradigm support and dynamic type systems, while ease of use comes from a simple syntax and rich standard library. 1. Flexibility: Supports object-oriented, functional and procedural programming, and dynamic type systems improve development efficiency. 2. Ease of use: The grammar is close to natural language, the standard library covers a wide range of functions, and simplifies the development process.

Python: The Power of Versatile ProgrammingPython: The Power of Versatile ProgrammingApr 17, 2025 am 12:09 AM

Python is highly favored for its simplicity and power, suitable for all needs from beginners to advanced developers. Its versatility is reflected in: 1) Easy to learn and use, simple syntax; 2) Rich libraries and frameworks, such as NumPy, Pandas, etc.; 3) Cross-platform support, which can be run on a variety of operating systems; 4) Suitable for scripting and automation tasks to improve work efficiency.

Learning Python in 2 Hours a Day: A Practical GuideLearning Python in 2 Hours a Day: A Practical GuideApr 17, 2025 am 12:05 AM

Yes, learn Python in two hours a day. 1. Develop a reasonable study plan, 2. Select the right learning resources, 3. Consolidate the knowledge learned through practice. These steps can help you master Python in a short time.

See all articles

Hot AI Tools

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress AI Tool

Undress images for free

Clothoff.io

Clothoff.io

AI clothes remover

AI Hentai Generator

AI Hentai Generator

Generate AI Hentai for free.

Hot Article

R.E.P.O. Energy Crystals Explained and What They Do (Yellow Crystal)
1 months agoBy尊渡假赌尊渡假赌尊渡假赌
R.E.P.O. Best Graphic Settings
1 months agoBy尊渡假赌尊渡假赌尊渡假赌
Will R.E.P.O. Have Crossplay?
1 months agoBy尊渡假赌尊渡假赌尊渡假赌

Hot Tools

MinGW - Minimalist GNU for Windows

MinGW - Minimalist GNU for Windows

This project is in the process of being migrated to osdn.net/projects/mingw, you can continue to follow us there. MinGW: A native Windows port of the GNU Compiler Collection (GCC), freely distributable import libraries and header files for building native Windows applications; includes extensions to the MSVC runtime to support C99 functionality. All MinGW software can run on 64-bit Windows platforms.

Notepad++7.3.1

Notepad++7.3.1

Easy-to-use and free code editor

WebStorm Mac version

WebStorm Mac version

Useful JavaScript development tools

Dreamweaver Mac version

Dreamweaver Mac version

Visual web development tools

SublimeText3 Mac version

SublimeText3 Mac version

God-level code editing software (SublimeText3)