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

id	challengeType	videoId
5e9a093a74c4063ca6f7c15e	11	sTMN_pdI6S0

--description--

More resources:

- Notebook

--question--

--text--

What will the following code print out?

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

--hints--

--solutions--