freeCodeCamp/curriculum/challenges/chinese/08-data-analysis-with-python/data-analysis-with-python-course/data-cleaning-with-dataframes.md

id, title, challengeType, isHidden, videoId

id	title	challengeType	isHidden	videoId
5e9a093a74c4063ca6f7c15e	Data Cleaning with DataFrames	11	false	sTMN_pdI6S0

Description

More resources: - Notebook

Tests

question:
  text: |
    What will the following code print out?

    ```py
    import pandas as pd
    import numpy as np

    s = pd.Series([np.nan, 1, 2, np.nan, 3])
    s = s.fillna(method='ffill')

    print(s)
    ```

  answers:
    - |
      ```
      0    1.0
      1    1.0
      2    2.0
      3    3.0
      4    3.0
      dtype: float64
      ```
    - |
      ```
      0    NaN
      1    1.0
      2    2.0
      3    2.0
      4    3.0
      dtype: float64
      ```
    - |
      ```
      0    NaN
      1    1.0
      2    2.0
      3    NaN
      4    3.0
      dtype: float64
      ```
  solution: 2