Indexes as columns

[TomAugspurger]

How to handle e.g.

df.pipe(ck.within_set, items={'A': [1, 2]})

But instead of the column A you want the index. Do we

• look for A, if it's not found, check if df.index.name == 'A'?
• allow mapping {'index': []} as a special case?
• create new functions like index_within_set?

[jnmclarty]

+1 for "look for A, if it's not found, check if df.index.name == 'A'?"