python - Produce a summary ("pivot"?) table

Question

I'd like a way to summarise a database table so that rows sharing a common ID are summarised into one row of output.

My tools are SQLite and Python 2.x.

For example, given the following table of fruit prices at my local supermarkets...

+--------------------+--------------------+--------------------+
|Fruit               |Shop                |Price               |
+--------------------+--------------------+--------------------+
|Apple               |Coles               |$1.50               |
|Apple               |Woolworths          |$1.60               |
|Apple               |IGA                 |$1.70               |
|Banana              |Coles               |$0.50               |
|Banana              |Woolworths          |$0.60               |
|Banana              |IGA                 |$0.70               |
|Cherry              |Coles               |$5.00               |
|Date                |Coles               |$2.00               |
|Date                |Woolworths          |$2.10               |
|Elderberry          |IGA                 |$10.00              |
+--------------------+--------------------+--------------------+

... I want to produce a summary table showing me the price of each fruit at each supermarket. Blank spaces should be filled by NULLs.

+----------+----------+----------+----------+
|Fruit     |Coles     |Woolworths|IGA       |
+----------+----------+----------+----------+
|Apple     |$1.50     |$1.60     |$1.70     |
|Banana    |$0.50     |$0.60     |$0.70     |
|Cherry    |NULL      |$5.00     |NULL      |
|Date      |$2.00     |$2.10     |NULL      |
|Elderberry|NULL      |NULL      |$10.00    |
+----------+----------+----------+----------+

I believe the literature calls this a "pivot table" or a "pivot query", but apparently SQLite doesn't support PIVOT. (The solution in that question uses hardcoded LEFT JOINs. This doesn't really appeal to me because I don't know the "column" names in advance.)

Right now I do this by iterating through the entire table in Python and accumulating a dict of dicts, which is a bit klutzy. I am open to better solutions, either in Python or SQLite, that will give the data in tabular form.

Answer 1

The pandas package can handle this very nicely.

>>> import pandas
>>> df=pandas.DataFrame(data, columns=['Fruit', 'Shop', 'Price'])
>>> df.pivot(index='Fruit', columns='Shop', values='Price')
Shop        Coles   IGA  Woolworths
Fruit                              
Apple         1.5   1.7         1.6
Banana        0.5   0.7         0.6
Cherry        5.0   NaN         NaN
Date          2.0   NaN         2.1
Elderberry    NaN  10.0         NaN

The documentation: http://pandas.pydata.org/pandas-docs/stable/reshaping.html

Some IPython Notebooks to learn pandas: https://bitbucket.org/hrojas/learn-pandas

Hope that will help.
Regards
Patrick Brockmann