python pandas dataframe aggregate groupby
<p>I have pandas DataFrame with many rows and columns, only three rows shown here:</p>

<pre><code>date    place    number
2010    LON      10
2010    BER      20
2010    LON      5
2011    LON      10
2011    BER      15
2011    BER      10
</code></pre>

<p>I want to make a new dataframe which aggregates by year and sums up the number according to place:</p>

<pre><code>date   place    number
2010   LON      15
2010   BER      20
2011   LON      10
2011   BER      25
</code></pre>

<p>I have tried many combinations of groupby with sum, inplace etc.  But I cannot achieve this, any suggestions?</p>