ENH: Add axis parameter to add_prefix and add_suffix

[Brinkhuis]

Feature Type

• Adding new functionality to pandas

• Changing existing functionality in pandas

• Removing existing functionality in pandas

Problem Description

df.add_prefix and df.add_suffix can be used on columns only.
Would be super handy if it can be used on the index to.
Preferably with the option inplace.

Example:

import pandas as pd
import numpy as np

np.random.seed(123)
data = np.random.randint(0, 100, size=(4, 3))
df = pd.DataFrame(data, index=range(1, 5), columns=range(20, 23))
df.index.name = 'Quarter'

DataFrame:

         20  21  22
Quarter            
1        66  92  98
2        17  83  57
3        86  97  96
4        47  73  32

New feature:

df.add_prefix('Q', axis=0, inplace=True)
df.add_prefix(20, axis=1, inplace=True)

Expected result:

         2020  2021  2022
Quarter                  
Q1         66    92    98
Q2         17    83    57
Q3         86    97    96
Q4         47    73    32

Implementation suggestion:

# columns
if df.columns is RangeIndex:
    df.columns = df.columns + 2000 # df.columns stays RangeIndex
else:
   df = df.add_prefix(20) # df.columns becomes list of integers

# index
if df.index is RangeIndex:
    df.set_index(df.index + 2000, inplace=True)
if all(isinstance(idx, int) for idx in list(df.index)): # df.index is list of integers
    df.set_index([int(str(prefix) + str(idx)) for idx in df.index], inplace=True)
else:
    df.set_index([str(prefix) + str(idx) for idx in df.index], inplace=True)

Feature Description

df.add_prefix('Q', axis=0, inplace=True)
df.add_prefix(20, axis=1, inplace=True)

Alternative Solutions

Implementation suggestion:

# columns
if df.columns is RangeIndex:
    df.columns = df.columns + 2000 # df.columns stays RangeIndex
else:
   df = df.add_prefix(20) # df.columns becomes list of integers

# index
if df.index is RangeIndex:
    df.set_index(df.index + 2000, inplace=True)
if all(isinstance(idx, int) for idx in list(df.index)): # df.index is list of integers
    df.set_index([int(str(prefix) + str(idx)) for idx in df.index], inplace=True)
else:
    df.set_index([str(prefix) + str(idx) for idx in df.index], inplace=True)

Additional Context

No response

[mroeschke]

Sounds reasonable to add an axis parameter; however, pandas is trying to move away from inplace so -1 on adding that parameter

[whym1here]

new df.add_prefix and df.add_suffix needs to implemented for all the data types and it needs to implemented in https://github.com/pandas-dev/pandas/blob/main/pandas/core/frame.py under class DataFrame(NDFrame, OpsMixin): ? (it possible can you provide a reference for a similar feature which has been added)@mroeschke

[jbrockmendel]

A copy kwarg would be good

[dannyi96]

this sounds nice.
Could i try working on this ? @mroeschke @jbrockmendel
Since as mentioned that we are moving away from inplace, can work on the change of supporting the axis parameter.

[ PS - @still-n0thing: is this is something you would like to work on / are already working on ]

[whym1here]

@dannyi96 I haven't started working on it. You could take up this issue if you want to.