[FEA] Add_suffix and add_prefix for DataFrames and Series

[beckernick]

Pandas provides add_suffix and add_prefix methods on DataFrames and Series. add_suffix. For API compatibility, it would be useful to implement them.

"For Series, the row labels are prefixed (suffixed). For DataFrame, the column labels are prefixed (suffixed)." [0].

If the labels are numeric, they are coerced to strings before concatenation.

[0] https://pandas.pydata.org/docs/reference/api/pandas.DataFrame.add_prefix.html

import pandas as pd
​
df = pd.DataFrame({'A': [1, 2, 3, 4], 'B': [3, 4, 5, 6]})
​
print(df)
print(df.add_suffix("_hello"))
print(df["A"])
print(df["A"].add_suffix("_hello"))
   A  B
0  1  3
1  2  4
2  3  5
3  4  6
   A_hello  B_hello
0        1        3
1        2        4
2        3        5
3        4        6
0    1
1    2
2    3
3    4
Name: A, dtype: int64
0_hello    1
1_hello    2
2_hello    3
3_hello    4
Name: A, dtype: int64