Index.intersection bug? · Issue #8362 · pandas-dev/pandas (original) (raw)

I ran into an odd behaviour when taking the intersection of two Indexes. Specifically,

left = pd.Index(['A','B','A','C']) right = pd.Index(['B','D']) left.intersection(right)

returns

Index(['B', 'C'], dtype='object')

However, I would expect this to return

Index(['B'], dtype='object')

If Index(['B', 'C'], dtype='object') is the intended behaviour, can someone explain the rationale behind it?