  The low frequency array (LOFAR), is the first radio telescope designed with
the capability to measure radio emission from cosmic-ray induced air showers in
parallel with interferometric observations. In the first $\sim
2\,\mathrm{years}$ of observing, 405 cosmic-ray events in the energy range of
$10^{16} - 10^{18}\,\mathrm{eV}$ have been detected in the band from $30 -
80\,\mathrm{MHz}$. Each of these air showers is registered with up to
$\sim1000$ independent antennas resulting in measurements of the radio emission
with unprecedented detail. This article describes the dataset, as well as the
analysis pipeline, and serves as a reference for future papers based on these
data. All steps necessary to achieve a full reconstruction of the electric
field at every antenna position are explained, including removal of radio
frequency interference, correcting for the antenna response and identification
of the pulsed signal.
