freeCodeCamp/curriculum/challenges/english/08-data-analysis-with-python/data-analysis-with-python-c.../data-cleaning-with-datafram...

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---
id: 5e9a093a74c4063ca6f7c15e
title: Data Cleaning with DataFrames
challengeType: 11
videoId: sTMN_pdI6S0
---
# --description--
*Instead of using notebooks.ai like it shows in the video, you can use Google Colab instead.*
More resources:
- [Notebooks on GitHub](https://github.com/ine-rmotr-curriculum/data-cleaning-rmotr-freecodecamp)
- [How to open Notebooks from GitHub using Google Colab.](https://colab.research.google.com/github/googlecolab/colabtools/blob/master/notebooks/colab-github-demo.ipynb)
# --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
```
## --video-solution--
2