I mean, isn't it groupby(), not group_by()?

On checking I found my polars version :

pl.__version__

0.17.3

https://pola-rs.github.io/polars/py-polars/html/reference/dataframe/api/polars.DataFrame.groupby.html

I need to do:

df.groupby("a").agg(pl.col("b").sum())  # there is no underscore in groupby

#output

shape: (3, 2)
a   b
str i64
"a" 2
"c" 3
"b" 5

and the document says :

Deprecated since version 0.19.0: This method has been renamed to DataFrame.group_by().

This is the new document for polars version 0.19

https://pola-rs.github.io/polars/py-polars/html/reference/dataframe/api/polars.DataFrame.group_by.html#polars-dataframe-group-by

DataFrame has no attribute group. However, it is possible to access data in a column in your dataframe with the same syntax used to access attributes and methods, i.e. if you have a column col, you may access the series related to this column through

df.col

What happened here is that your data is probably different from what she used in the tutorial. Or at least, the columns she has are different than the columns you have.

To solve that problem, you can either (I) simply rename your columns to match the columns from the tutorial or (II) replace data.group with the corresponding column name that you have in your df

the solution is to use a loc to set the values, rather than creating a copy.

creating a copy of df loses the name:

df = df[::-1] # creates a copy

setting the value 'keeps' the original object intact, along with name

df.loc[:] = df[:, ::-1] # reversal maintaining the original object

Example code that reverses values along the column axis:

df = pd.DataFrame([[6,10]], columns=['a','b'])
df.name='t'
print(df.name)
print(df)
df.iloc[:] = df.iloc[:,::-1]
print(df)
print(df.name)

outputs:

t
   a   b
0  6  10
    a  b
0  10  6
t