pandas.melt() is used to convert wide format data into long format. The answer is to define new column names by specifying id_vars retain the identification column, value_vars select the columns to be melted, var_name and value_name. 1. id_vars='Name' means that the Name column remains unchanged, 2. value_vars=['Math','English','Science'] specifies the columns to be melted, 3. var_name='Subject' sets the new column name of the original column name, 4. value_name='Score' sets the new column name of the original value, and finally generates long-form data containing three columns Name, Subject and Score, which is suitable for subsequent visualization and analysis. This operation melts all other columns by default when value_vars is not specified, and is often used in seaborn drawing and other scenarios.
pandas.melt()
is a very practical function for converting data in wide-format to long-format, which is often used in data cleaning and visualization preprocessing. The following is a simple example to illustrate the usage of melt
.

Assume that there is the following wide format data:
import pandas as pd df = pd.DataFrame({ 'Name': ['Alice', 'Bob', 'Charlie'], 'Math': [85, 90, 78], 'English': [88, 75, 82], 'Science': [92, 85, 80] }) print(df)
Output:
Name Math English Science 0 Alice 85 88 92 1 Bob 90 75 85 2 Charlie 78 82 80
In this table, each course is a column and the data is "wide". If we want to turn it into two columns "Article" and "Score" to facilitate subsequent drawing or analysis, we can use melt
.

Use melt()
to convert to a long format
df_melted = pd.melt( df, id_vars='Name', # Keep unchanged columns (identify variables) value_vars=['Math', 'English', 'Science'], # column to "melt" var_name='Subject', # new variable name value_name='Score' # new value column name) print(df_melted)
Output:
Name Subject Score 0 Alice Math 85 1 Bob Math 90 2 Charlie Math 78 3 Alice English 88 4 Bob English 75 5 Charlie English 82 6 Alice Science 92 7 Bob Science 85 8 Charlie Science 80
Parameter description
-
id_vars
: column that is not melted as an identifier (such asName
here) -
value_vars
: columns that need to be melted (optional, if not filled in, the default is all columns exceptid_vars
) -
var_name
: The variable name that becomes the original column name after melting (default isvariable
) -
value_name
: After melting, the column name corresponding to the original value (default isvalue
)
? Tips: If you do not specify
value_vars
, pandas will automatically melt all columns exceptid_vars
.
For example:
df_melted = pd.melt(df, id_vars='Name')
The effect is the same as above.
Practical application scenarios
- When making bar charts/line charts, libraries such as seaborn usually require data to be in long format.
- Comparison of the grade distributions of different subjects
- Structure of time series data merged from multiple columns into time values
For example, use seaborn to draw pictures:
import seaborn as sns import matplotlib.pyplot as plt sns.barplot(data=df_melted, x='Name', y='Score', hue='Subject') plt.show()
Basically that's it. melt
is not complicated, but it is particularly practical, especially when you are facing a wide table of "one column, one variable", melt will be refreshing.
The above is the detailed content of python pandas melt example. For more information, please follow other related articles on the PHP Chinese website!

Hot AI Tools

Undress AI Tool
Undress images for free

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Clothoff.io
AI clothes remover

Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Article

Hot Tools

Notepad++7.3.1
Easy-to-use and free code editor

SublimeText3 Chinese version
Chinese version, very easy to use

Zend Studio 13.0.1
Powerful PHP integrated development environment

Dreamweaver CS6
Visual web development tools

SublimeText3 Mac version
God-level code editing software (SublimeText3)

To realize text error correction and syntax optimization with AI, you need to follow the following steps: 1. Select a suitable AI model or API, such as Baidu, Tencent API or open source NLP library; 2. Call the API through PHP's curl or Guzzle and process the return results; 3. Display error correction information in the application and allow users to choose whether to adopt it; 4. Use php-l and PHP_CodeSniffer for syntax detection and code optimization; 5. Continuously collect feedback and update the model or rules to improve the effect. When choosing AIAPI, focus on evaluating accuracy, response speed, price and support for PHP. Code optimization should follow PSR specifications, use cache reasonably, avoid circular queries, review code regularly, and use X

User voice input is captured and sent to the PHP backend through the MediaRecorder API of the front-end JavaScript; 2. PHP saves the audio as a temporary file and calls STTAPI (such as Google or Baidu voice recognition) to convert it into text; 3. PHP sends the text to an AI service (such as OpenAIGPT) to obtain intelligent reply; 4. PHP then calls TTSAPI (such as Baidu or Google voice synthesis) to convert the reply to a voice file; 5. PHP streams the voice file back to the front-end to play, completing interaction. The entire process is dominated by PHP to ensure seamless connection between all links.

When choosing a suitable PHP framework, you need to consider comprehensively according to project needs: Laravel is suitable for rapid development and provides EloquentORM and Blade template engines, which are convenient for database operation and dynamic form rendering; Symfony is more flexible and suitable for complex systems; CodeIgniter is lightweight and suitable for simple applications with high performance requirements. 2. To ensure the accuracy of AI models, we need to start with high-quality data training, reasonable selection of evaluation indicators (such as accuracy, recall, F1 value), regular performance evaluation and model tuning, and ensure code quality through unit testing and integration testing, while continuously monitoring the input data to prevent data drift. 3. Many measures are required to protect user privacy: encrypt and store sensitive data (such as AES

Use Seaborn's jointplot to quickly visualize the relationship and distribution between two variables; 2. The basic scatter plot is implemented by sns.jointplot(data=tips,x="total_bill",y="tip",kind="scatter"), the center is a scatter plot, and the histogram is displayed on the upper and lower and right sides; 3. Add regression lines and density information to a kind="reg", and combine marginal_kws to set the edge plot style; 4. When the data volume is large, it is recommended to use "hex"

The core idea of PHP combining AI for video content analysis is to let PHP serve as the backend "glue", first upload video to cloud storage, and then call AI services (such as Google CloudVideoAI, etc.) for asynchronous analysis; 2. PHP parses the JSON results, extract people, objects, scenes, voice and other information to generate intelligent tags and store them in the database; 3. The advantage is to use PHP's mature web ecosystem to quickly integrate AI capabilities, which is suitable for projects with existing PHP systems to efficiently implement; 4. Common challenges include large file processing (directly transmitted to cloud storage with pre-signed URLs), asynchronous tasks (introducing message queues), cost control (on-demand analysis, budget monitoring) and result optimization (label standardization); 5. Smart tags significantly improve visual

To integrate AI sentiment computing technology into PHP applications, the core is to use cloud services AIAPI (such as Google, AWS, and Azure) for sentiment analysis, send text through HTTP requests and parse returned JSON results, and store emotional data into the database, thereby realizing automated processing and data insights of user feedback. The specific steps include: 1. Select a suitable AI sentiment analysis API, considering accuracy, cost, language support and integration complexity; 2. Use Guzzle or curl to send requests, store sentiment scores, labels, and intensity information; 3. Build a visual dashboard to support priority sorting, trend analysis, product iteration direction and user segmentation; 4. Respond to technical challenges, such as API call restrictions and numbers

The core of PHP's development of AI text summary is to call external AI service APIs (such as OpenAI, HuggingFace) as a coordinator to realize text preprocessing, API requests, response analysis and result display; 2. The limitation is that the computing performance is weak and the AI ecosystem is weak. The response strategy is to leverage APIs, service decoupling and asynchronous processing; 3. Model selection needs to weigh summary quality, cost, delay, concurrency, data privacy, and abstract models such as GPT or BART/T5 are recommended; 4. Performance optimization includes cache, asynchronous queues, batch processing and nearby area selection. Error processing needs to cover current limit retry, network timeout, key security, input verification and logging to ensure the stable and efficient operation of the system.

String lists can be merged with join() method, such as ''.join(words) to get "HelloworldfromPython"; 2. Number lists must be converted to strings with map(str, numbers) or [str(x)forxinnumbers] before joining; 3. Any type list can be directly converted to strings with brackets and quotes, suitable for debugging; 4. Custom formats can be implemented by generator expressions combined with join(), such as '|'.join(f"[{item}]"foriteminitems) output"[a]|[
