Top-level Koalas functions - merge

[itholic]

Resolves #961

>>> df1 = ks.DataFrame({'lkey': ['foo', 'bar', 'baz', 'foo'],
...                     'value': [1, 2, 3, 5]},
...                    columns=['lkey', 'value'])
>>> df2 = ks.DataFrame({'rkey': ['foo', 'bar', 'baz', 'foo'],
...                     'value': [5, 6, 7, 8]},
...                    columns=['rkey', 'value'])
>>> df1
  lkey  value
0  foo      1
1  bar      2
2  baz      3
3  foo      5
>>> df2
  rkey  value
0  foo      5
1  bar      6
2  baz      7
3  foo      8

>>> merged = ks.merge(df1, df2, left_on='lkey', right_on='rkey')
>>> merged.sort_values(by=['lkey', 'value_x', 'rkey', 'value_y'])
  lkey  value_x rkey  value_y
0  bar        2  bar        6
5  baz        3  baz        7
1  foo        1  foo        5
2  foo        1  foo        8
3  foo        5  foo        5
4  foo        5  foo        8

>>> left_kdf = ks.DataFrame({'A': [1, 2]})
>>> right_kdf = ks.DataFrame({'B': ['x', 'y']}, index=[1, 2])

>>> ks.merge(left_kdf, right_kdf, left_index=True, right_index=True)
   A  B
1  2  x

>>> ks.merge(left_kdf, right_kdf, left_index=True, right_index=True, how='left')
   A     B
0  1  None
1  2     x

>>> ks.merge(left_kdf, right_kdf, left_index=True, right_index=True, how='right')
     A  B
1  2.0  x
2  NaN  y

>>> ks.merge(left_kdf, right_kdf, left_index=True, right_index=True, how='outer')
     A     B
0  1.0  None
1  2.0     x
2  NaN     y

[codecov-io]

Codecov Report

Merging #969 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master     #969   +/-   ##
=======================================
  Coverage   94.57%   94.57%           
=======================================
  Files          34       34           
  Lines        6487     6487           
=======================================
  Hits         6135     6135           
  Misses        352      352

Impacted Files	Coverage Δ
databricks/koalas/namespace.py	87.26% <100%> (+0.11%)	⬆️
databricks/koalas/frame.py	96.02% <0%> (-0.01%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update b2286bd...afe5066. Read the comment docs.

[ueshin]

Shall we add a link to docs/source/reference/general_functions.rst?

Otherwise, LGTM.

[itholic]

@ueshin Thanks for the comment! just added it

[softagram-bot]

Softagram Impact Report for pull/969 (head commit: afe5066)

⭐ Change Overview

(Open in Softagram Desktop for full details)

📄 Full report

• Permalink: Full report for pull/969

Impact Report explained. Give feedback on this report to [email protected]