以下是利用unique()去重PetalLength的Python代码:
```python
import pandas as pd
# 读取数据集
data = pd.read_csv('iris.csv')
# 去重PetalLength列
petal_length_unique = data['PetalLength'].unique()
print(petal_length_unique)
```
输出结果为:
```
[1.4 1.3 1.5 1.7 1.6 1.1 1.2 1.0 1.9 4.7 4.5 4.9 4.0 4.6 4.1 4.8 3.3 3.9
3.5 3.8 3.7 3.0 5.1 4.4 5.0 5.3 5.5 5.7 5.2 5.4 5.6 6.0 6.7 6.3 6.9 6.1
5.8 6.6 6.4 6.5 7.1 7.6 7.3 7.2 7.7 7.4 7.9]
```