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numpy/numpy#15555 reports an issue with np.argwhere on pandas Series. Reporting here for visibility.

MRE:

>>> import numpy as np >>> import pandas as pd >>> s = pd.Series(np.random.randn(5), index=['a', 'b', 'c', 'd', 'e']) >>> np.argwhere(s < 0)

which, with numpy.__version__ ==1.20.0.dev0+046a736 gives:
pd.version == 0.25.3:

FutureWarning: Series.nonzero() is deprecated and will be removed in a future version.Use Series.to_numpy().nonzero() instead array([[3]]) 

pd.version == 1.0.5:

ValueError: Length of passed values is 1, index implies 5.