Find Row Mismatch for Index

Question

I have a multi index pandas df that looks like the image below. The Group is the main index. Each group represents a group of duplicate files. The file number is a unique identifier for each file. Value 1 and Value 2 are metadata fields in this example.

What I would like to do is find instances where ANY metadata across a group is inconsistent.

For example, in the below image, Group 1 would return because File Numbers 1 and 2 in group A1 have differing metadata under 'Value 1' - so I would want that group to return. Group A2 on the other hand wouldn't return as the metadata IS consistent.

Is there a way to generate this dataframe?

df = pd.read_csv('files.csv', index_col = ['Group', 'File Number'])

Answer 1

Use groupby with nunique

tuples = [('A1',1),('A1',2),('A2',3),('A2',4)]
index = pd.MultiIndex.from_tuples(tuples, names=["Group", "File Number"])
value1 = ['A','B','D','D']
df = pd.DataFrame(data=value1,index=index, columns=['Value1'])

df.groupby('Group').nunique()

Data frame:

Now, using df.groupby('Group').nunique() gives

    Value1
Group   
A1  2
A2  1

Answer 2

You can use groupby_nunique and broadcast the output to all rows. Finally, find rows where at least one value is not consistent:

out = df[df.groupby(level='Group').transform('nunique').ne(1).any(axis=1)]
print(out)

# Output
                  Value 1 Value 2
Group File Number                
A1    1                 A       C
      2                 B       C