title: which() function in R
body: <p>I have a data <code>frame(A)</code> of size (92047x2) and a <code>list(B)</code> of size (1829). I want to create a new data frame with all rows of A whose first column value is present in B.</p>
  <p>How to use <code>which()</code>? Or any other good way to approach this?</p>
  <p>All the values are in form of character. (Eg. &quot;Vc2345&quot;)</p>