DOC: Correct uniqueness of index for Series

[themrmax]

closes #7808

Just wanted to fix the docstring to reflect the fact that the index labels neither need to be unique nor hashable.

[chris-b1]

It is true that labels no longer need to be unique, but they still must be hashable?

[themrmax]

No they don't need to be hashable currently:

In [5]: s = pd.Series ([1,2,3], index = ([1],[1],[1]))

In [6]: s
Out[6]:
[1]    1
[1]    2
[1]    3
dtype: int64

Do you think we should add a check for hashable?

[jreback]

try to index that and see what happens

[themrmax]

@jreback lol i don't know, maybe some people use series without ever indexing them? otherwise do you think we should add a check for hashable values? Or maybe edit the doco to say "for the object to support indexing, the labels must be of a hashable type"?

[jreback]

In [4]: s = pd.Series ([1,2,3], index = ([1],[2],[3]))

In [5]: s.loc[[1]]
TypeError: unhashable type: 'list'

In [7]: s.index.inferred_type
Out[7]: 'mixed'

So we do actually check hashable, but its fairly lazy as its somewhat to expensive to do this. The point is that this is non-idiomatic, and though may work in parts of pandas is not supported, nor recommended in any way.

So if you'd like to update with a stronger warning would be great.

[jorisvandenbossche]

@themrmax Can you update this? (leave out the hashable change for now, but you can keep the change regarding uniqueness)

[jreback]

spacing here

[themrmax]

ah sorry about just learned how to use textwidth in vim

[codecov-io]

Current coverage is 85.21% (diff: 100%)

Merging #14344 into master will decrease coverage by 0.04%

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[jorisvandenbossche]

This line is too long (therefore travis is failing, we test for PEP8 (line length < 80))

[themrmax]

ah sorry about this i got my < confused with my ≤, i'll set my linewidth to 79.

[jorisvandenbossche]

@themrmax Thanks!
(I added one sentence from another PR for the same issue ("Non-unique index values are allowed") before merging)

[themrmax]

cool thanks @jorisvandenbossche yes that's clearer now !