set multi index of an existing data frame in pandas

Question

I have a DataFrame that looks like

  Emp1    Empl2           date       Company
0    0        0     2012-05-01         apple
1    0        1     201         


        

Answer 1

When you pass inplace in makes the changes on the original variable and returns None, and the function does not return the modified dataframe, it returns None.

is_none = df.set_index(['Company', 'date'], inplace=True)
df  # the dataframe you want
is_none # has the value None

so when you have a line like:

df = df.set_index(['Company', 'date'], inplace=True)

it first modifies df... but then it sets df to None!

That is, you should just use the line:

df.set_index(['Company', 'date'], inplace=True)