Combine different columns into a new column in a dataframe using pandas

Question

I have a sample dataframe of a very huge dataframe as given below.

import pandas as pd
import numpy as np

NaN = np.nan

data = {'Start_x':['Tom', NaN, NaN, NaN,NaN],
    'Start_y':[NaN, 'Nick', NaN, NaN, NaN],
    'Start_z':[NaN, NaN, 'Alison', NaN, NaN],
    'Start_a':[NaN, NaN, NaN, 'Mark',NaN],
    'Start_b':[NaN, NaN, NaN, NaN, 'Oliver'],
    'Sex': ['Male','Male','Female','Male','Male']}

df = pd.DataFrame(data)
df

I want the final result to look like the image given below. The 4 columns have to be merged to a single new column but the 'Sex' column should be as it is.

Any help is greatly appreciated. Thank you!

Answer 1

One option could be to backfill Start columns by rows and then take the first column:

df['New_Column'] = df.filter(like='Start').bfill(axis=1).iloc[:, 0]

df
  Start_x Start_y Start_z Start_a Start_b     Sex New_Column
0     Tom     NaN     NaN     NaN     NaN    Male        Tom
1     NaN    Nick     NaN     NaN     NaN    Male       Nick
2     NaN     NaN  Alison     NaN     NaN  Female     Alison
3     NaN     NaN     NaN    Mark     NaN    Male       Mark
4     NaN     NaN     NaN     NaN  Oliver    Male     Oliver