擅长:python、mysql、java
<h2><code>str.split</code>+<code>groupby</code>+<code>count</code></h2>
<pre><code>df.groupby(df['timstamp'].str.split().str[0])._id.count().reset_index()
timstamp _id
0 2018-05-09 2
1 2018-05-10 1
2 2018-05-11 2
</code></pre>
<hr/>
<h2><code>to_datetime</code>+<code>groupby</code>+<code>count</code></h2>
^{pr2}$
<p>或者</p>
<pre><code>df['timstamp'] = pd.to_datetime(df['timstamp']).dt.floor('D')
df.groupby('timstamp', as_index=False)._id.count()
</code></pre>
<p/>
<pre><code> timstamp _id
0 2018-05-09 2
1 2018-05-10 1
2 2018-05-11 2
</code></pre>