Reduce the number of joins for mod/rmod.

[ueshin]

This is a follow-up of #1399.

When performing mod/rmod, if the operands are series from different dataframes, we needed three joins.

>>> kser = ks.Series([100, None, -300, None, 500, -700], name="Koalas")
>>> (kser % ks.Series([150] * 6)).to_frame().explain()
== Physical Plan ==
*(9) Project [CASE WHEN isnotnull(__index_level_0__#317L) THEN __index_level_0__#317L ELSE __index_level_0__#228L END AS __index_level_0__#378L, (Koalas#364 % cast(0#229L as double)) AS Koalas#425]
+- SortMergeJoin [__index_level_0__#317L], [__index_level_0__#228L], FullOuter
   :- *(7) Sort [__index_level_0__#317L ASC NULLS FIRST], false, 0
   :  +- Exchange hashpartitioning(__index_level_0__#317L, 200)
   :     +- *(6) Project [CASE WHEN isnotnull(__index_level_0__#254L) THEN __index_level_0__#254L ELSE __index_level_0__#228L END AS __index_level_0__#317L, (Koalas#303 + cast(0#229L as double)) AS Koalas#364]
   :        +- SortMergeJoin [__index_level_0__#254L], [__index_level_0__#228L], FullOuter
   :           :- *(4) Sort [__index_level_0__#254L ASC NULLS FIRST], false, 0
   :           :  +- Exchange hashpartitioning(__index_level_0__#254L, 200)
   :           :     +- *(3) Project [CASE WHEN isnotnull(__index_level_0__#0L) THEN __index_level_0__#0L ELSE __index_level_0__#228L END AS __index_level_0__#254L, (Koalas#1 % cast(0#229L as double)) AS Koalas#303]
   :           :        +- SortMergeJoin [__index_level_0__#0L], [__index_level_0__#228L], FullOuter
   :           :           :- *(1) Sort [__index_level_0__#0L ASC NULLS FIRST], false, 0
   :           :           :  +- Exchange hashpartitioning(__index_level_0__#0L, 200)
   :           :           :     +- Scan ExistingRDD[__index_level_0__#0L,Koalas#1]
   :           :           +- *(2) Sort [__index_level_0__#228L ASC NULLS FIRST], false, 0
   :           :              +- Exchange hashpartitioning(__index_level_0__#228L, 200)
   :           :                 +- Scan ExistingRDD[__index_level_0__#228L,0#229L]
   :           +- *(5) Sort [__index_level_0__#228L ASC NULLS FIRST], false, 0
   :              +- ReusedExchange [__index_level_0__#228L, 0#229L], Exchange hashpartitioning(__index_level_0__#228L, 200)
   +- *(8) Sort [__index_level_0__#228L ASC NULLS FIRST], false, 0
      +- ReusedExchange [__index_level_0__#228L, 0#229L], Exchange hashpartitioning(__index_level_0__#228L, 200)

We can reduce the number to only one.

>>> (kser % ks.Series([150] * 6)).to_frame().explain()
== Physical Plan ==
*(3) Project [CASE WHEN isnotnull(__index_level_0__#0L) THEN __index_level_0__#0L ELSE __index_level_0__#98L END AS __index_level_0__#118L, (((Koalas#1 % cast(0#99L as double)) + cast(0#99L as double)) % cast(0#99L as double)) AS Koalas#165]
+- SortMergeJoin [__index_level_0__#0L], [__index_level_0__#98L], FullOuter
   :- *(1) Sort [__index_level_0__#0L ASC NULLS FIRST], false, 0
   :  +- Exchange hashpartitioning(__index_level_0__#0L, 200)
   :     +- Scan ExistingRDD[__index_level_0__#0L,Koalas#1]
   +- *(2) Sort [__index_level_0__#98L ASC NULLS FIRST], false, 0
      +- Exchange hashpartitioning(__index_level_0__#98L, 200)
         +- Scan ExistingRDD[__index_level_0__#98L,0#99L]

[ueshin]

cc @itholic

[codecov-io]

Codecov Report

Merging #1409 into master will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1409      +/-   ##
==========================================
- Coverage   95.03%   95.01%   -0.02%     
==========================================
  Files          34       34              
  Lines        7952     7950       -2     
==========================================
- Hits         7557     7554       -3     
- Misses        395      396       +1     

Impacted Files	Coverage Δ
databricks/koalas/base.py	97.57% <100.00%> (+0.78%)	⬆️
databricks/koalas/series.py	96.96% <0.00%> (-0.37%)	⬇️

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[itholic]

Thanks, I feel learning a lot from this work.
LGTM. 👍

[ueshin]

Thanks! I'd merge this now. Please feel free to leave comments.

[itholic]

Got it!