f='https://rdrr.io/r/base/list.html'>list</a></span><span class='op'>(</span>ncol <span class='op'>=</span> <span class='fu'>data.table</span><span class='fu'>::</span><span class='fu'><a href='https://Rdatatable.gitlab.io/data.table/reference/J.html'>CJ</a></span><span class='op'>(</span>x <span class='op'>=</span> <span class='fl'>1</span><span class='op'>:</span><span class='fl'>50</span>, y <span class='op'>=</span> <span class='va'>letters</span><span class='op'>[</span><span class='fl'>1</span><span c