title: How to get integer row names of a data frame/matrix in R?
body: <p>I have a data frame A in which <code>max(A$user_id)=23000</code>. Also <code>typeof(A$user_id)=integer</code>. I made a data frame B with <code>rownames(B)=unique(A$user_id)</code> and <code>colnames(B)=unique(A$product_id)</code>. However, when I check <code>max(rownames(B))</code>, it comes out to be <code>999</code>. I did <code>row names(B)&lt;-as.integer(rownames(B))</code>. But still, 
  <code>max(rownames(B))=999</code>.What should I do to convert the rownames to integer? I want this because I want to fill up B according to rownames.</p>