r "Data Set Basics", section "Multi-file NetCDF data sets".</p>
<p align="left">Beginning with Ferret/PyFerret v7, the command <strong><a href="../commands-reference/DEFINE.html#_define_data_agg" title="DEFINE">TSERIES</a></strong> (an alias for DEFINE DATA/T) may be used as an alternative to multi-CDF datasets. This command defines an aggregation in the time direction, creating a virtual dataset in the Ferret session. Each method has advantages. Multi-file datasets will initialize more quickly than making 