Generate all combinations, of all lengths, in R, from a vector
<p>Suppose I have the vector <code>["a","b","c"]</code>, then I'd like to create a list of vectors of all the <strong>unique</strong> combinations, of all sizes (order does not matter):</p>

<pre><code>["a"]
["b"]
["c"]
["a","b"]
["a","c"]
["b","c"]
["a","b","c"]
</code></pre>

<p>How can I do this in R?</p>