tps://github.com/hadley/nycflights13" class="external-link">nycflights13</a></span><span class="op">)</span></span>
<span><span class="kw"><a href="https://rdrr.io/r/base/library.html" class="external-link">library</a></span><span class="op">(</span><span class="va"><a href="https://github.com/hadley/reshape" class="external-link">reshape2</a></span><span class="op">)</span></span>
<span><span class="va">mtcars.grp</span><span class="op">[[</span><span class="st">"mtcars"</span><span class="op">]</span><spa