remove duplicate values based on 2 columns
<p>I want to remove duplicate values based upon matches in 2 columns in a dataframe, <code>v2</code> &amp; <code>v4</code> must match between rows to be removed.</p>
<pre><code>&gt; df

   v1  v2  v3   v4  v5
1  7   1   A  100  98 
2  7   2   A  100  97
3  8   1   C   NA  80
4  8   1   C   78  75
5  8   1   C   78  62
6  9   3   C   75  75
</code></pre>
<p>For a result of</p>
<pre><code>&gt; df

   v1  v2  v3   v4  v5
1  7   1   A  100  98 
2  8   1   C   NA  80
3  8   1   C   78  75
4  9   3   C   75  75
</code></pre>
<p>I know I want something like:</p>
<pre><code>df[!duplicated(df[v2] &amp;&amp; df[v4]),] 
</code></pre>
<p>but this doesn't work.</p>
<p>This question is specifically about dataframes, for those who have a data.table, see <a href="https://stackoverflow.com/questions/11792527/filtering-out-duplicated-non-unique-rows-in-data-table">Filtering out duplicated/non-unique rows in data.table</a>.</p>