 class="usage"><span class='fu'>ncombinations</span>(<span class='kw'>x</span> <span class='kw'>=</span> <span class='kw'>NULL</span>, <span class='kw'>k</span> <span class='kw'>=</span> <span class='kw'>NULL</span>, <span class='kw'>n</span> <span class='kw'>=</span> <span class='kw'>NULL</span>, <span class='kw'>v</span> <span class='kw'>=</span> <span class='kw'>NULL</span>,
  <span class='kw'>freq</span> <span class='kw'>=</span> <span class='kw'>NULL</span>, <span class='kw'>replace</span> <span class=