pandas time-series data preprocessing
<p>I have dataframe look likes this :</p>

<pre><code>&gt; dt
    text    timestamp
0   a   2016-06-13 18:00
1   b   2016-06-20 14:08
2   c   2016-07-01 07:41
3   d   2016-07-11 19:07
4   e   2016-08-01 16:00
</code></pre>

<p>And I want to summarise every month's data like:</p>

<pre><code>&gt; dt_month
count   timestamp
0   2   2016-06
1   2   2016-07
2   1   2016-08
</code></pre>

<p>the original dataset(<code>dt</code>) can be generated by:</p>

<pre><code>import pandas as pd
data = {'text': ['a', 'b', 'c', 'd', 'e'],
    'timestamp': ['2016-06-13 18:00', '2016-06-20 14:08', '2016-07-01 07:41', '2016-07-11 19:07', '2016-08-01 16:00']}
dt = pd.DataFrame(data)
</code></pre>

<p>And are there any ways can plot a time-frequency plot by <code>dt_month</code> ?</p>