擅长:python、mysql、java
<p>另一种解决方案是将<code>birthdate</code>设置为索引并重新采样:</p>
<pre><code>import pandas as pd
df = pd.DataFrame({'birthdate': pd.date_range(start='20-12-2015', end='3-1-2016')})
df.set_index('birthdate').resample('MS').size()
</code></pre>
<p>输出:</p>
<pre class="lang-none prettyprint-override"><code>birthdate
2015-12-01 12
2016-01-01 31
2016-02-01 29
2016-03-01 1
Freq: MS, dtype: int64
</code></pre>