Pandas GroupBy - Show only groups with more than one unique feature-value

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I have a DataFrame df_things that looks like this and i want to predict the quality of the classification before the training

A    B     C      CLASS
-----------------------
al1  bal1  cal1   Ship
al1  bal1  cal1   Ship
al1  bal2  cal2   Ship
al2  bal2  cal2   Cow
al3  bal3  cal3   Car
al1  bal2  cal3   Car
al3  bal3  cal3   Car

I want to group rows by classes so that i have an idea of the distribution of the features. I do this with (for example, on col "B"), 

df_B = df_things.groupby('CLASS').B.value_counts()

which gives me the results

CLASS  B 
-------------
ship   bal1  2 
       bal2  1
cow    bal2  2
car    bal2  1
       bal3  2

What I want to to is to visualize only groups that have more than one value so that it looks like this:

CLASS  B 
-------------
ship   bal1  2 
       bal2  1
car    bal2  1
       bal3  2

I'm a little bit stuck, so any ideas?

pandas-groupby pandas compare unique python
2 Answers

You can use groupby to filter groups that have an nunique count over 1.

v = df_things.groupby('CLASS').B.value_counts()
v[v.groupby(level=0).transform('nunique').gt(1)]

CLASS  B   
Car    bal3    2
       bal2    1
Ship   bal1    2
       bal2    1
Name: B, dtype: int64
user_49090870

Solution from crosstab

s=pd.crosstab(df.CLASS,df.B)
s[s.ne(0).sum(1)>1].replace(0,np.nan).stack()
CLASS  B   
Car    bal2    1.0
       bal3    2.0
Ship   bal1    2.0
       bal2    1.0
dtype: float64
user_79645270
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