Make Index constructor take Series or Index objects.

[ueshin]

Makes Index constructor take Series or Index objects.

>>> kser = ks.Series([1, 2, 3], name="a", index=[10, 20, 30])
>>> ks.Index(kser)
Int64Index([1, 2, 3], dtype='int64', name='a')
>>> ks.Int64Index(kser)
Int64Index([1, 2, 3], dtype='int64', name='a')
>>> ks.Float64Index(kser)
Float64Index([1.0, 2.0, 3.0], dtype='float64', name='a')

>>> kser = ks.Series([datetime(2021, 3, 1), datetime(2021, 3, 2)], index=[10, 20])
>>> ks.Index(kser)
DatetimeIndex(['2021-03-01', '2021-03-02'], dtype='datetime64[ns]', freq=None)
>>> ks.DatetimeIndex(kser)
DatetimeIndex(['2021-03-01', '2021-03-02'], dtype='datetime64[ns]', freq=None)

[xinrong-meng]

Looks great, thank you!

[codecov-io]

Codecov Report

Merging #2071 (6dc9e9f) into master (0f6eb80) will decrease coverage by 0.14%.
The diff coverage is 96.66%.

@@            Coverage Diff             @@
##           master    #2071      +/-   ##
==========================================
- Coverage   94.68%   94.53%   -0.15%     
==========================================
  Files          55       55              
  Lines       11718    11747      +29     
==========================================
+ Hits        11095    11105      +10     
- Misses        623      642      +19     

Impacted Files	Coverage Δ
databricks/koalas/indexes/base.py	97.29% <93.33%> (-0.12%)	⬇️
databricks/koalas/base.py	97.53% <100.00%> (ø)
databricks/koalas/indexes/datetimes.py	92.85% <100.00%> (+1.55%)	⬆️
databricks/koalas/indexes/numeric.py	92.59% <100.00%> (+3.70%)	⬆️
databricks/koalas/typedef/typehints.py	91.62% <0.00%> (-2.80%)	⬇️
databricks/koalas/__init__.py	89.33% <0.00%> (-2.67%)	⬇️
databricks/conftest.py	98.55% <0.00%> (-1.45%)	⬇️
databricks/koalas/plot/matplotlib.py	91.63% <0.00%> (-0.37%)	⬇️
databricks/koalas/indexes/multi.py	93.47% <0.00%> (-0.35%)	⬇️
databricks/koalas/generic.py	93.03% <0.00%> (-0.22%)	⬇️
... and 4 more

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[ueshin]

Thanks! merging.

[xinrong-meng]

That's a great catch! :)