.. _auto_dataset_add_column_by_regexp:

*DATASET ADD COLUMN BY REGEXP*
==============================

Adds a new column to a dataset by extracting values from an existing column using a regular expression with capture groups. The matched substring (at the specified capture-group index) is stored in the new column for every row. Use this worker when you need to parse structured text embedded in a column — e.g., extracting a numeric dimension from a filename or label string.

When to use
-----------

Classification: **process**.

Tagged: ``add_column``, ``capture_group``, ``dataset_transform``, ``extract``, ``regex``, ``regexp``, ``string_parsing``.

Inputs
------

.. list-table::
   :header-rows: 1
   :widths: 20 20 20 20 20 20

   * - Label
     - ID
     - Type
     - Default
     - Required
     - Description
   * - Choose Dataset
     - dataset
     - dataset
     - —
     - 
     - Input dataset (tabular) whose rows will be processed; must contain the source column specified in 'column_name'.
   * - New Column Name
     - new_column_name
     - scalar
     - —
     - 
     - Name of the new column that will be appended to the dataset to hold the regex-extracted values.
   * - Column For Regex
     - column_name
     - scalar
     - —
     - 
     - Name of the existing column in the dataset whose cell values will be searched with the regular expression.
   * - Regular Expression
     - regexp
     - scalar
     - —
     - 
     - Regular expression (with at least one capture group) applied to each cell; e.g., '(\d+)_mm' extracts the digit sequence immediately preceding '_mm'.
   * - Choose Index
     - index
     - scalar
     - 1
     - 
     - 1-based index of the capture group whose match is written to the new column; defaults to 1 (first capture group).

Outputs
-------

.. list-table::
   :header-rows: 1
   :widths: 20 20 20 20

   * - Label
     - ID
     - Type
     - Description
   * - dataset_add_column_by_regexp_output_1
     - dataset_add_column_by_regexp_output_1
     - dataset
     - A copy of the input dataset with the new column appended, containing the regex-extracted substring for each row.

Disciplines
-----------

- data.dataset.transform

Runnable example
----------------

A runnable example is registered for this worker. Open the example workflow on the d3VIEW canvas: `/api/workflow/example?id=dataset_add_column_by_regexp <https://www.d3view.com/api/workflow/example?id=dataset_add_column_by_regexp>`_

.. raw:: html

   <hr style="margin-top:2em">
   <p style="font-size:11px;color:#888">
   Auto-generated from <code>transformation</code> schema. Worker id: <code>dataset_add_column_by_regexp</code>. Schema hash: <code>94ca0fbc9be2</code>. Hand-curated docs in <code>workerexamples/</code> override this page when present.
   </p>