Invalid fill method. expecting pad (ffill) or backfill (bfill). got linear

The error message “invalid fill method. expecting pad (ffill) or backfill (bfill). got linear” indicates that the fill method used is not correct. When specifying a fill method, it should be either “pad” (ffill) or “backfill” (bfill), but in this case, “linear” was used instead.

The fill method is often used in data manipulation to specify how missing values should be filled in a dataset. The “pad” method fills missing values with the previous non-null value, while the “backfill” method fills missing values with the next non-null value.

Here’s an example to illustrate the difference between “pad” and “backfill” methods:

    import pandas as pd
    import numpy as np

    data = {'A': [1, np.nan, 3, np.nan, 5]}
    df = pd.DataFrame(data)

    # Using pad method (ffill)
    df_pad = df.fillna(method='pad')
    print(df_pad)

    # Using backfill method (bfill)
    df_backfill = df.fillna(method='backfill')
    print(df_backfill)
  

Output:

    A
    0  1.0
    1  1.0
    2  3.0
    3  3.0
    4  5.0

    A
    0  1.0
    1  3.0
    2  3.0
    3  5.0
    4  5.0
  

In the above example, the “pad” method (ffill) fills missing values with the previous non-null value (1.0), while the “backfill” method (bfill) fills missing values with the next non-null value (3.0).