擅长:python、mysql、java
<p>我想你需要<a href="http://pandas.pydata.org/pandas-docs/stable/generated/pandas.core.groupby.GroupBy.transform.html" rel="nofollow noreferrer">^{<cd1>}</a>:</p>
<pre><code>df['class_size'] = df.groupby('class_name')['class_name'].transform('size')
</code></pre>
<p>或:</p>
<pre><code>df['class_size'] = df.groupby('class_name')['class_name'].transform('count')
</code></pre>
<p><a href="https://stackoverflow.com/questions/33346591/what-is-the-difference-between-size-and-count-in-pandas">What is the difference between size and count in pandas?</a></p>