擅长:python、mysql、java
<p>使用<code>transform</code>:</p>
<pre><code>full['DEM'] = full.groupby('state')['demVote'].transform('mean')
</code></pre>
<p><strong>例如:</strong></p>
<pre><code>>>> full
demVote state
0 1 ca
1 2 ca
2 3 ny
3 4 ny
full['DEM'] = full.groupby('state')['demVote'].transform('mean')
>>> full
demVote state DEM
0 1 ca 1.5
1 2 ca 1.5
2 3 ny 3.5
3 4 ny 3.5
</code></pre>