lass="r-out co"><span class="r-pr">#&gt;</span> 2  o  o  o  o</span>
<span class="r-out co"><span class="r-pr">#&gt;</span> 5  X  X  X  X</span>
<span class="r-out co"><span class="r-pr">#&gt;</span> 3  o  o  o  o</span>
<span class="r-out co"><span class="r-pr">#&gt;</span> 6  X  X  X  X</span>
<span class="r-in"><span></span></span>
<span class="r-in"><span><span class="co"># data frames unequal in no. of rows</span></span></span>
<span class="r-in"><span><span class="va">df1</span> <span class="op">&lt;-