calculation is particularly expensive).  One way to force the column
efficiently is to clone it:</p>
<pre><code class="language-clojure">user&gt; (ds/head (ds/update-column stocks-lag "price-lag" dtype/clone))
test/data/stocks.csv [5 4]:

| symbol |       date | price | price-lag |
|--------+------------+-------+-----------|
|   MSFT | 2000-01-01 | 39.81 |     39.81 |
|   MSFT | 2000-02-01 | 36.35 |     39.81 |
|   MSFT | 2000-03-01 | 43.22 |     36.35 |
|   MSFT | 2000-04-01 | 28.37 |     43.22 |
|   MSFT 