Added stochastic gradient boosting algorithm
Added stochastic gradient boosting algorithm
Code refactor
Added test 'StochasticGradientBoostingSuite'
Added new test
Refactor tests
Merge branch 'gradient_boosting' of https://github.com/olgaoskina/spark into olgaoskina-gradient_boosting
t push origin master:Merge branch 'olgaoskina-gradient_boosting' into SPARK-3507
[SPARK-3525] Fixing GradientBoostingSuite