pythonpandascompareuniquepandas-groupby

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

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?

Solution

  • 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