def convert_string_to_list(df, col, new_col):
    """Convert column from string to list format."""
    fxn = lambda arr_string: [int(item) for item in str(arr_string).split(" ")]

    mask = ~(df[col].isnull())

    df[new_col] = df[col]
    df.loc[mask, new_col] = df[mask][col].map(fxn)

    return df