pandas - Why am I getting column headers for each index of a dataframe in Python?

Question

Hi so currently I am trying to create an empty dataframe in python using this code:

for i in range (len('bus0')):
    empty_df = pd.DataFrame(np.nan, index=[i], columns=['bus0', 'bus1'])
    print(empty_df)

But I am getting an output (below) which reprints the column headers bus0 and bus1 for each index in the dataframe:

 bus0  bus1
0   NaN   NaN
   bus0  bus1
1   NaN   NaN
   bus0  bus1
2   NaN   NaN
   bus0  bus1
3   NaN   NaN

I do not want the column headers to keep reappearing for each index, I just want them to show up once at the top. How does one achieve this?

question from:https://stackoverflow.com/questions/65831090/why-am-i-getting-column-headers-for-each-index-of-a-dataframe-in-python

Answer 1

There are a few things going on. You're both reassigning and reprinting the dataframe every time you go through the for loop.

To see what I mean, the following code (just taking the print statement out of the for loop) only prints the last data assigned to the dataframe.

for i in range (len('bus0')):
    empty_df = pd.DataFrame(np.nan, index=[i], columns=['bus0', 'bus1'])

# print(empty_df)
'''
bus0  bus1
3   NaN   NaN
'''

Instead of reassigning the whole dataframe, I would declare it before the for loop and just add each row in the for loop using .iloc. You can also use .iloc to assign different values to different rows while iterating through the for loop.

import pandas as pd
import numpy as np

empty_df = pd.DataFrame(columns=['bus0', 'bus1'])

for i in range (len('bus0')):
    empty_df.loc[i] = np.nan

# print(empty_df)
'''
bus0 bus1
0  NaN  NaN
1  NaN  NaN
2  NaN  NaN
3  NaN  NaN
'''