> ## Documentation Index
> Fetch the complete documentation index at: https://docs.clickml.app/llms.txt
> Use this file to discover all available pages before exploring further.

# Concatenate DataFrames component

> Stack two DataFrames vertically to add more rows or horizontally to add more columns, with control over index alignment and join behavior.

The **Concatenate** component appends one DataFrame to another along a chosen axis — useful for combining datasets that share the same schema, or for adding new columns.

## Configuration

| Option           | Description                                                                                    | Default |
| ---------------- | ---------------------------------------------------------------------------------------------- | ------- |
| **Axis**         | `Rows (vertical stack)` — adds rows. `Columns (horizontal stack)` — adds columns side by side. | Rows    |
| **Ignore Index** | Reset the row index in the result                                                              | Yes     |
| **Join**         | `outer` keeps all columns (fills NaN for missing). `inner` keeps only shared columns.          | `outer` |

## Input / Output

|        | Type                               |
| ------ | ---------------------------------- |
| Input  | First DataFrame + Second DataFrame |
| Output | DataFrame                          |

## When to use

* **Vertical (rows):** Combine two CSV files that have the same columns (e.g. January data + February data).
* **Horizontal (columns):** Attach a new set of columns to an existing DataFrame when rows are already aligned.