擅长:python、mysql、java
<p>我会用<a href="https://pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.merge.html" rel="nofollow noreferrer">merge</a></p>
<pre class="lang-py prettyprint-override"><code>avg_df = trainDf.groupby(by='User_ID')['Purchase_Amount'].mean().reset_index().rename(columns={'Purchase_Amount': 'Avg'})
trainDf = trainDf.merge(avg_df, on='User_ID')
</code></pre>