an>-&gt;<span class="num">4</span>)</pre><p>If there is a one-to-one relationship between offset i and key (ie, no duplicate
keys in the index), you may achieve the same effect via key as follows:</p><pre>f.first(<span class="num">0</span>) == Series(<span class="lit">'a'</span>-&gt;<span class="num">1</span>, <span class="lit">'b'</span>-&gt;<span class="num">4</span>)
f.firstCol(<span class="lit">'a'</span>) == Series(<span class="num">1</span>,<span class="num">2</span>,<span class="num">3</span>)</pre><