uded in the returned
<a href='https://www.rdocumentation.org/packages/data.table/topics/data.table'>data.table</a>.</p></li>
<li><p><code>period</code>: A Date or POSIXt vector used to specify which time period to
return. The year value does not matter and only month, day, hour and
minute value will be used when subsetting. If <code>NULL</code>, all time period of
data is returned. Default: <code>NULL</code>.</p></li>
<li><p><code>month</code>, <code>day</code>, <code>hour</code>, <code>minute</code>: Each 