.. index:: Core Operations; Aggregate Attachment
.. _core-operation-aggregate-attachment:

AggregateAttachment
==================================

Applies an aggregate attachment to the sum of a group of records that share
equal values for their ``Trial`` field. It is applied incrementally to groups of records
that share same values for ``Trial``, ``Time``, and ``OccurrenceKey`` fields. Once the
attachment is applied, the result is proportionally allocated to all records in
the group.

Structure
---------

.. code-block:: json

    {
        "_schema": "AggregateAttachment_1.0",
        "attachment": 1000,
        "currency": "GBP"
    }

Parameters
----------

+----------------------+----------+------------------+--------------------------------------------------------------+
| Parameter Name       | Required | Type             | Description                                                  |
+======================+==========+==================+==============================================================+
| ``attachment``       | Yes      | ``double``       | The attachment value in currency units. Cannot be negative.  |
+----------------------+----------+------------------+--------------------------------------------------------------+
| ``currency``         | No       | ``string``       | The currency in which ``attachment`` is defined.             |
+----------------------+----------+------------------+--------------------------------------------------------------+

Behaviour
--------------

This is equivalent to :doc:`scoped_attachment` with
``span_columns`` set to ``[]`` and ``erode_columns`` set to
``[Time, OccurrenceKey]``.
In other words, it applies an eroding attachment that erodes over the
entire trial to occurrences generated by combining records with matching
``Time`` and ``OccurrenceKey`` values.