擅长:python、mysql、java
<p>使用<code>groupby</code>查找<code>first</code>和<code>last</code>,然后<code>merge</code>返回原始df</p>
<pre class="lang-py prettyprint-override"><code>df2 = df.groupby(['T_Id']).agg({'StartReading' : 'first', 'EndReading' : 'last'}).reset_index(0)
df2['Diff'] = df2['EndReading'] - df2['StartReading']
df.merge(df2[['T_Id', 'Diff']], how='left', on='T_Id')
</code></pre>