How to add an indicator column for concat in pandas?

Question

With merge() there is an indicator parameter so you can identify from which df you the original data is found. I don't see a similar function withconcat().

pd.merge(left=df1, right=df2, indicator=True)

Is there a way to create an indicator column with concat()?

Answer 1

import pandas as pd

df1 = pd.DataFrame(['a','b'], index=[0,1], columns=['letter'])
df2 = pd.DataFrame(['c','d','e'], index=[2,3,4], columns=['letter'])
result = pd.concat([df1, df2], axis=0, keys=['from_df1','from_df2']).reset_index(level=[0])

df1

  letter
0      a
1      b

df2

  letter
2      c
3      d
4      e

result

    level_0 letter
0  from_df1      a
1  from_df1      b
2  from_df2      c
3  from_df2      d
4  from_df2      e

Answer 2

I ended up creating a new column labeled FileName in each file, then I concat().

df1['FileName'] = 'df1'
df2['FileName'] = 'df2'


final = pd.concat(df1,df2)

Column1   Column2   Column3  FileName
3         89        08       df1
43        934       34       df1
34        934       32       df2
431       2342      23       df2