.. _gwpy-example-table-rate:

.. sectionauthor:: Duncan Macleod <duncan.macleod@ligo.org>

.. currentmodule:: gwpy.table

Calculating (and plotting) rate versus time for an `EventTable`
###############################################################

I would like to study the rate at which event triggers are generated by the
`ExcessPower` gravitational-wave burst detection algorithm, over a small
stretch of data.

The data from which these events were generated contain a simulated
gravitational-wave signal, or hardware injection, used to validate
the performance of the LIGO detectors and downstream data analysis procedures.

First, we import the `EventTable` object and read in a set of events from
a LIGO_LW-format XML file containing a
:class:`sngl_burst <ligo.lw.lsctables.SnglBurstTable>` table

.. plot::
   :context: reset
   :nofigs:
   :include-source:

   from gwpy.table import EventTable
   events = EventTable.read('H1-LDAS_STRAIN-968654552-10.xml.gz',
                            tablename='sngl_burst', columns=['peak', 'snr'])

.. note::

   Here we manually specify the `columns` to read in order to optimise
   the `read()` operation to parse only the data we actually need.

We can calculate the rate of events (in Hertz) using the
:meth:`~EventTable.event_rate` method:

.. plot::
   :context:
   :nofigs:
   :include-source:

   rate = events.event_rate(1, start=968654552, end=968654562)

The :meth:`~EventTable.event_rate` method has returned a
`~gwpy.timeseries.TimeSeries`, so we can display this using the
:meth:`~gwpy.timeseries.TimeSeries.step` method of that object:

.. plot::
   :context:
   :include-source:

   plot = rate.step()
   ax = plot.gca()
   ax.set_xlim(968654552, 968654562)
   ax.set_ylabel('Event rate [Hz]')
   ax.set_title('LIGO Hanford Observatory event rate for HW100916')
   plot.show()