DataFrame.pivot without index argument should preserve the original index names.

[ueshin]

DataFrame.pivot without index argument should preserve the original index names.

>>> import pandas as pd
>>> pdf = pd.DataFrame({"foo": ['one', 'one', 'two', 'two'], "bar": ['A', 'A', 'B', 'C'], "baz": [1, 2, 3, 4]}, columns=['foo', 'bar', 'baz'])
>>> pdf.index.name = 'x'
>>> pdf
   foo bar  baz
x
0  one   A    1
1  one   A    2
2  two   B    3
3  two   C    4
>>> pdf.pivot(columns='bar', values='baz')
bar    A    B    C
x
0    1.0  NaN  NaN
1    2.0  NaN  NaN
2    NaN  3.0  NaN
3    NaN  NaN  4.0

whereas:

>>> ks.from_pandas(pdf).pivot(columns='bar', values='baz').sort_index()
bar    A    B    C
0    1.0  NaN  NaN
1    2.0  NaN  NaN
2    NaN  3.0  NaN
3    NaN  NaN  4.0

[codecov-io]

Codecov Report

Merging #1316 into master will decrease coverage by 2.34%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1316      +/-   ##
==========================================
- Coverage   95.23%   92.89%   -2.35%     
==========================================
  Files          34       34              
  Lines        7331     7332       +1     
==========================================
- Hits         6982     6811     -171     
- Misses        349      521     +172

Impacted Files	Coverage Δ
databricks/koalas/frame.py	93.55% <100%> (-3.17%)	⬇️
databricks/koalas/usage_logging/__init__.py	24.32% <0%> (-71.18%)	⬇️
databricks/koalas/usage_logging/usage_logger.py	50% <0%> (-50%)	⬇️
databricks/koalas/__init__.py	78.72% <0%> (-14.9%)	⬇️
databricks/conftest.py	88.67% <0%> (-7.55%)	⬇️
databricks/koalas/namespace.py	86.3% <0%> (-1.49%)	⬇️
databricks/koalas/plot.py	93.33% <0%> (-0.96%)	⬇️
databricks/koalas/testing/utils.py	78.26% <0%> (-0.73%)	⬇️
databricks/koalas/groupby.py	91.22% <0%> (-0.22%)	⬇️
... and 1 more

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[HyukjinKwon]

Nice, LGTM!