gsub() everything except specified characters?
<p>How do I gsub() everything except a specified character in R?</p>

<p>In my problem I have the following string...</p>

<pre><code>"the quick brown fox jumps over a lazy dog"
</code></pre>

<p>I have to generate a new string with by removing all characters except 'r' and 'o' and get the following output...</p>

<pre><code>"roooro"
</code></pre>

<p>Assuming all characters are lower case how do I go about. I tried...</p>

<pre><code>gsub(!"r","",gsub(!"o","",str1))
</code></pre>

<p>But the '!' doesn't work.</p>