如何在分类类型上设置索引？

Question

鉴于此 Dask DataFrame ：

Dask DataFrame Structure:
             date  value           symbol
npartitions=2                                
           object  int64  category[known]
...              ...
...              ...
Dask Name: from-delayed, 6 tasks2130

如何在“符号”列（类别[已知）上设置索引？

df = df.set_index('symbol')
Traceback (most recent call last):
[...]
TypeError: Categorical is not ordered for operation max
you can use .as_ordered() to change the Categorical to an ordered one

Answer 1

分类对象必须先按顺序定义，然后才能对其建立索引。错误消息告诉我们使用as_ordered(). 这个方法来自于cat结构体：

df['symbol'] = df['symbol'].cat.as_ordered()
df = df.set_index('symbol')