> For the complete documentation index, see [llms.txt](https://senselab.gitbook.io/senselab-docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://senselab.gitbook.io/senselab-docs/vendor/sanmai/pipeline/docs/quickstart/walkthrough.md).

# Walkthrough: Processing CSV Data

This walkthrough demonstrates the core concepts of the library by building a practical data processing pipeline.

## The Goal

Our objective is to process a string of CSV data. We will parse the data, skip the header, transform it into a more usable format, filter it based on a condition, and finally, collect the results.

## The Pipeline

Here is the complete pipeline:

```php
use function Pipeline\take;

// Sample CSV data with a header row
$csv = <<<CSV
name,age,city
Alice,30,New York
Bob,25,Los Angeles
Charlie,35,Chicago
David,28,New York
CSV;

// Build the pipeline
$users = take(explode("\n", $csv))
    ->map(str_getcsv(...))        // 1. Parse each line into an array
    ->slice(1)                    // 2. Skip the header row
    ->map(fn($row) => [          // 3. Transform to an associative array
        'name' => $row[0],
        'age' => (int)$row[1],
        'city' => $row[2]
    ])
    ->filter(fn($user) => $user['age'] >= 30)  // 4. Keep users aged 30 or over
    ->toList();                   // 5. Execute the pipeline and collect results

// The final result:
// [
//   ['name' => 'Alice', 'age' => 30, 'city' => 'New York'],
//   ['name' => 'Charlie', 'age' => 35, 'city' => 'Chicago']
// ]
```

## Step-by-Step Explanation

1. **`take(explode("\n", $csv))`**: We begin by creating a pipeline from the CSV data. `explode()` splits the string into an array of lines.
2. **`map(str_getcsv(...))`**: The `map()` method is used to apply `str_getcsv()` to each line, converting each CSV string into an array of values.
3. **`slice(1)`**: This method skips the first element of the pipeline, which in this case is the header row.
4. **`map(fn($row) => ...)`**: We use `map()` again to transform the indexed array for each row into a more readable associative array.
5. **`filter(fn($user) => ...)`**: The `filter()` method is used to apply our business logic, keeping only the users who are 30 years of age or older.
6. **`toList()`**: This is a terminal operation. It triggers the execution of all the previous (lazy) operations and collects the final results into an array.

## Key Concepts

This example illustrates several core principles of the library:

* **Lazy Evaluation**: No processing occurs until a terminal method like `toList()` is called.
* **Method Chaining**: Each operation returns the pipeline object, allowing for a fluent and expressive syntax.
* **Transformation**: `map()` is used to change the structure and format of the data.
* **Filtering**: `filter()` and `slice()` are used to selectively remove data.

## Next Steps

* Explore the [Cookbook](/senselab-docs/vendor/sanmai/pipeline/docs/cookbook/index.md) for more practical examples.
* Consult the [API Reference](/senselab-docs/vendor/sanmai/pipeline/docs/api/creation.md) for detailed information on each method.


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://senselab.gitbook.io/senselab-docs/vendor/sanmai/pipeline/docs/quickstart/walkthrough.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.