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---
id: 5e9a093a74c4063ca6f7c15e
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title: Data Cleaning with DataFrames
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challengeType: 11
videoId: sTMN_pdI6S0
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dashedName: data-cleaning-with-dataframes
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---
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# --description--
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*Instead of using notebooks.ai like it shows in the video, you can use Google Colab instead.*
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More resources:
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- [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 )
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# --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--
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< pre >
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0 1.0
1 1.0
2 2.0
3 3.0
4 3.0
dtype: float64
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< / pre >
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---
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< pre >
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0 NaN
1 1.0
2 2.0
3 2.0
4 3.0
dtype: float64
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< / pre >
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---
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< pre >
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0 NaN
1 1.0
2 2.0
3 NaN
4 3.0
dtype: float64
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< / pre >
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## --video-solution--
2