pandas.crosstab中缺少数据

Question

I'm making some crosstabs with pandas:

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)

pd.crosstab(a, [b, c], rownames=['a'], colnames=['b', 'c'])

b     one   two       
c    dull  dull  shiny
a                     
bar     1     1      0
foo     2     1      2

But what I actually want is the following:

b     one        two       
c    dull  shiny dull  shiny
a                     
bar     1     0    1      0
foo     2     0    1      2

I found workaround by adding new column and set levels as new MultiIndex, but it seems to be difficult...

Is there any way to pass MultiIndex to crosstabs function to predefine output columns?

Answer 1

The crosstab function has a parameter called dropna which is set to True by default. This parameter defines whether empty columns (such as the one-shiny column) should be displayed or not.

I tried calling the funcion like this:

pd.crosstab(a, [b, c], rownames=['a'], colnames=['b', 'c'], dropna = False)

and this is what I got:

b     one          two       
c    dull  shiny  dull  shiny
a                            
bar     1      0     1      0
foo     2      0     1      2

Hope that was still helpful.

Answer 2

I don't think there is a way to do this, and crosstab calls pivot_table in the source, which doesn't seem to offer this either. I raised it as an issue here .

A hacky workaround (which may or may not be the same as you were already using...):

from itertools import product
ct = pd.crosstab(a, [b, c], rownames=['a'], colnames=['b', 'c'])
a_x_b = list(product(np.unique(b), np.unique(c)))
a_x_b = pd.MultiIndex.from_tuples(a_x_b)

In [15]: ct.reindex_axis(a_x_b, axis=1).fillna(0)
Out[15]:
      one          two
     dull  shiny  dull  shiny
a
bar     1      0     1      0
foo     2      0     1      2

If product is too slow, here is a numpy implementation of it.