"><span><span class="fu">zipFastener</span><span class="op">(</span><span class="va">df2</span>, <span class="va">df1</span>, <span class="fl">2</span><span class="op">)</span></span></span>
<span class="r-out co"><span class="r-pr">#&gt;</span>    V1 V1.1 V2 V2.1 V3 V3.1 V4</span>
<span class="r-out co"><span class="r-pr">#&gt;</span> 1   X    o  X    o  X    o  o</span>
<span class="r-out co"><span class="r-pr">#&gt;</span> 2   X    o  X    o  X    o  o</span>
<span class="r-out co"><span class="r-pr">#&g