Pandas使用时间索引筛选时报错 AssertionError: <class 'numpy.ndarray'>

I came across the similar problem, my solution was:

1. make sure the index is type of 'DatetimeIndex', I do this:

df.index = pd.to_datetime(df.index)

2. sorted the 'index' first：

df = df.sort_index()

And then operations (below) should work:

df_sub = df['2018']  # select the whole year of 2018

df_sub2 = df['2018-02']  # select the given month

df_sub3 = df['2018-01':'2018-03']  # select between dates

来源：https://stackoverflow.com/questions/64106628/why-assertionerror-having-numpy-ndarray