How can an array be added as a separate column to a CSV file using numpy (preferable) or python 3 without overwriting the CSV file or data?

Question

The new data to be appended has a shorter length!

Here is an example:

Add numpy array:
ema  =  [3.3  3.4  3.5  3.6]

                                            (csv now has 3-columns of equal length)
1.1  2.1    append  ema  to end up with:    1.1  2.1  0
1.2  2.2                                    1.2  2.2  0
1.3  2.3                                    1.3  2.3  3.3
1.4  2.4                                    1.4  2.4  3.4
1.5  2.5                                    1.5  2.5  3.5
1.6  2.6                                    1.6  2.6  3.6

Answer 1

@kinshukdua's comment suggestion as code:

Best way would be to read the old data as a pandas dataframe and then append the column to it and fill empty columns with 0s and finally writing it back to csv.

using this

import pandas as pd
my_csv_path = r"path/to/csv.csv"
df = pd.read_csv(my_csv_path)
ema_padded = np.concatenate([np.zeros(len(df) - ema.shape[0]), ema])
df['ema'] = pd.Series(ema_padded, index=df.index)
df.to_csv(my_csv_path)

Answer 2

df.to_csv(file_path, index=False)