Partitioning segmentations
==========================

There are many situations where we might want so selectively in- or exclude
segments from a segmentation. For instance, a user might be want to exclude
from a word segmentation all those that are less than 4 letters long. The
:ref:`Select` widget is tailored for such tasks.

The widget's interface (see :ref:`figure 1 <partitioning_segmentations_fig1>`
below) offers a choice between two modes: *Include* and *Exclude*. Depending
on this parameter, incoming segments that satisfy a given condition will be
either included in or excluded from the output segmentation. By default (i.e.
when the **Advanced settings** box is unchecked), the condition is specified
by means of a regex, which will be applied to each incoming segment
successively. (For now, the option **Annotation key: (none)** can be ignored.)

.. _partitioning_segmentations_fig1:

.. figure:: figures/select_example.png
    :align: center
    :alt: Example usage of widget Select
    :figclass: align-center

    Figure 1: Excluding short words with widget :ref:`Select`.

In the example of :ref:`figure 1 <partitioning_segmentations_fig1>`, the
widget is configured to exclude all incoming segments containing no more than
3 letters. Note that without the *beginning of segment* and *end of segment*
anchors (``^`` and ``$``), all words containing *at least* a sequence of 1 to
3 letters--i.e. all the words--would be excluded.

Note that :ref:`Select` automatically emits a second segmentation
containing all the segments that have been discarded from the main output
segmentation (in the case of :ref:`figure 1 <partitioning_segmentations_fig1>`
above, that would be all words less than 4 letters long). This feature is
useful when both the selected *and* the discarded segments are to be further
processed on distinct branches. By default, when :ref:`Select` is connected to
another widget, the main segmentation is being emitted. In order to send the
segmentation of discarded segments instead, right-click on the outgoing
connection and select **Reset Signals** (see
:ref:`figure 2 <partitioning_segmentations_fig2>` below).

.. _partitioning_segmentations_fig2:

.. figure:: figures/select_example_schema.png
    :align: center
    :alt: Right-clicking on a connection and requesting to "Reset Signals"
    :figclass: align-center
    :scale: 80 %

    Figure 2: Right-clicking on a connection and requesting to **Reset Signals**.

This opens the dialog shown on
:ref:`figure 3 <partitioning_segmentations_fig3>` below, where the user can
"drag-and-drop" from the gray box next to **Discarded data** up to the box
next to **Segmentation**, thus replacing the existing green connection.
Clicking **OK** validates the modification and sends the discarded data
through the connection.

.. _partitioning_segmentations_fig3:

.. figure:: figures/select_example_reset_signals_dialog.png
    :align: center
    :alt: Dialog for modifying the connection between two widgets
    :figclass: align-center
    :scale: 80 %

    Figure 3: This dialog allows the user to select a non-default connection between two widgets.


