Add min_count parameter for Frame.sum.

[ueshin]

Adds min_count parameter for Frame.sum.

[codecov-io]

Codecov Report

Merging #1978 (f4a976e) into master (c973195) will decrease coverage by 0.99%.
The diff coverage is 96.87%.

@@            Coverage Diff             @@
##           master    #1978      +/-   ##
==========================================
- Coverage   94.56%   93.57%   -1.00%     
==========================================
  Files          50       50              
  Lines       10935    10946      +11     
==========================================
- Hits        10341    10243      -98     
- Misses        594      703     +109     

Impacted Files	Coverage Δ
databricks/koalas/frame.py	96.75% <92.85%> (-0.04%)	⬇️
databricks/koalas/generic.py	91.89% <100.00%> (-0.24%)	⬇️
databricks/koalas/series.py	96.91% <100.00%> (+<0.01%)	⬆️
databricks/koalas/testing/utils.py	80.71% <100.00%> (+0.19%)	⬆️
databricks/koalas/usage_logging/__init__.py	24.78% <0.00%> (-67.53%)	⬇️
databricks/koalas/usage_logging/usage_logger.py	47.82% <0.00%> (-52.18%)	⬇️
databricks/koalas/__init__.py	81.25% <0.00%> (-9.38%)	⬇️
databricks/conftest.py	94.20% <0.00%> (-5.80%)	⬇️
databricks/koalas/utils.py	93.59% <0.00%> (-1.78%)	⬇️
... and 2 more

---

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 c973195...f4a976e. Read the comment docs.

[itholic]

Cool. LGTM

[itholic]

+1

[xinrong-meng]

Are we going to add test cases in a separate pr?

[ueshin]

I'll fix some corner cases and add tests soon.

[xinrong-meng]

Great! LGTM!

[ueshin]

Thanks! merging.