DataFrame of DataFrames in Python (Pandas)
<p>The idea here is that for every year, I am able to create three dataframes(df1, df2, df3), each containing different firms and stock prices('firm' and 'price' are the two columns in df1~df3). I would like to use another dataframe (named 'store' below) to store the three dataframes every year.</p>

<p>Here is what I code:</p>

<pre><code>store = pd.DataFrame(list(range(1967,2014)), columns=['year'])
for year in range(1967,2014):
    ....some codes that allow me to generate df1, df2 and df3 correctly...
    store.loc[store['year']==year, 'df1']=df1
    store.loc[store['year']==year, 'df2']=df2
    store.loc[store['year']==year, 'df3']=df3
</code></pre>

<p>I am not getting error warning or anything after this code. 
But in the "store" dataframe, columns 'df1', 'df2' and 'df3' are all 'NAN' values.</p>