pydata/pandas — pull request #4106 by hayd (2013-07-02 18:16:57+00:00)
Title: ENH add drop_na argument to pivot_table

fixes #3820

```
a = np.array(['foo', 'foo', 'foo', 'bar', 'bar', 'foo', 'foo'], dtype=object)
b = np.array(['one', 'one', 'two', 'one', 'two', 'two', 'two'], dtype=object)
c = np.array(['dull', 'dull', 'dull', 'dull', 'dull', 'shiny', 'shiny'], dtype=object)

In [11]: pd.crosstab(a, [b, c], rownames=['a'], colnames=['b', 'c'], drop_na=False)
Out[11]:
b one two
c dull shiny dull shiny
a
bar 1 0 1 0
foo 2 0 1 2
```

Also same argument for `pivot_table`.