## What changes were proposed in this pull request?
RandomForest R Wrapper and GBT R Wrapper return param `maxDepth` to R models.
Below 4 R wrappers are changed:
* `RandomForestClassificationWrapper`
* `RandomForestRegressionWrapper`
* `GBTClassificationWrapper`
* `GBTRegressionWrapper`
## How was this patch tested?
Test manually on my local machine.
Author: Xin Ren <iamshrek@126.com>
Closes#17207 from keypointt/SPARK-19282.
## What changes were proposed in this pull request?
spark.lda passes the optimizer "em" or "online" as a string to the backend. However, LDAWrapper doesn't set optimizer based on the value from R. Therefore, for optimizer "em", the `isDistributed` field is FALSE, which should be TRUE based on scala code.
In addition, the `summary` method should bring back the results related to `DistributedLDAModel`.
## How was this patch tested?
Manual tests by comparing with scala example.
Modified the current unit test: fix the incorrect unit test and add necessary tests for `summary` method.
Author: wm624@hotmail.com <wm624@hotmail.com>
Closes#16464 from wangmiao1981/new.
## What changes were proposed in this pull request?
SparkR ```mllib.R``` is getting bigger as we add more ML wrappers, I'd like to split it into multiple files to make us easy to maintain:
* mllib_classification.R
* mllib_clustering.R
* mllib_recommendation.R
* mllib_regression.R
* mllib_stat.R
* mllib_tree.R
* mllib_utils.R
Note: Only reorg, no actual code change.
## How was this patch tested?
Existing tests.
Author: Yanbo Liang <ybliang8@gmail.com>
Closes#16312 from yanboliang/spark-18862.
