title: equivalent of a python dict in R
body: <p>I want to make the equivalent of a python dict in R. Basically in python, I have:</p>
  <pre><code>visited = {}
  
  if atom_count not in visited:
    Do stuff
    visited[atom_count] = 1
  </code></pre>
  <p>The idea is, if I saw that specific, atom_count, I have <code>visited[atom_count] = 1</code>. Thus, if I see that atom_count again, then I don't &quot;Do Stuff&quot;. <code>Atom_Count</code> is an integer.</p>
  <p>Thanks!</p>