擅长:python、mysql、java
<p>其工作原理与:</p>
<pre><code>no_user_voted = ratings.groupby('movieId')['rating'].count()
</code></pre>
<p>这意味着对于列<code>movieId</code>(组)的每个值,聚合函数<a href="http://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.core.groupby.GroupBy.count.html" rel="nofollow noreferrer">^{<cd3>}</a>只对列<code>rating</code>的所有缺失值进行计数</p>
<p>区别在于只有<code>count</code>函数被传递给代码中的<a href="http://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.core.groupby.GroupBy.agg.html" rel="nofollow noreferrer">^{<cd5>}</a></p>