/summarise_dt.html">summarise_dt</a></span><span class="op">(</span>m_arr <span class="op">=</span> <span class="fu"><a href="https://rdrr.io/r/base/mean.html" class="external-link">mean</a></span><span class="op">(</span><span class="va">arr_delay</span><span class="op">)</span>, m_dep <span class="op">=</span> <span class="fu"><a href="https://rdrr.io/r/base/mean.html" class="external-link">mean</a></span><span class="op">(</span><span class="va">dep_delay</span><span class="op">)</span><span class="op">)