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

---
id: 5e9a093a74c4063ca6f7c15e
title: Data Cleaning with DataFrames
challengeType: 11
isHidden: true
videoId: sTMN_pdI6S0
---

## Description
<section id='description'>
</section>

## Tests
<section id='tests'>

```yml
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
```

</section>