xgboost: expose watchlist and callbacks

[khotilov]

• expose watchlist and callbacks through parameters classif.xgboost - error if early.stop.round is set? #1264
• remove silent from the parameters - it's overridden by verbose in xgboost R interface and has no effect
• set default lambda=1 as it is such for tree boosters
  • Question: is there any way to conditionally set default lambda=0 when booster=='gblinear'?
• add tweedie_variance_power parameter
• placeholders for some recently added parameters (commented out until the next CRAN release)

[lintr-bot]

R/RLearner_classif_xgboost.R:43:7: style: TODO comments should be removed.

​      # TODO: uncomment the following after the next CRAN update, and set max_depth's lower = 0L
      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

R/RLearner_regr_xgboost.R:43:7: style: TODO comments should be removed.

​      # TODO: uncomment the following after the next CRAN update, and set max_depth's lower = 0L
      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

[larskotthoff]

@mb706 Can we have the lintr allow TODO comments please?

[mb706]

that would be direct violation of the style guide <https://github.com/rdatsci/PackagesInfo/wiki/R-Style-Guide> point 17 ;-) Anhway, to disable this, comment out the "todo.comment" linter here: <https://github.com/mlr-org/mlr/blob/master/tests/testthat/helper_lint.R#L269>

…

On June 20, 2017 4:13:43 PM GMT+02:00, Lars Kotthoff ***@***.***> wrote: @mb706 Can we have the lintr allow TODO comments please?

[larskotthoff]

That style point doesn't apply here -- it's a todo for when a new package version is released. The style guide doesn't say anything about not allowing TODOs in general.

[khotilov]

TODO codetags have fairly different semantics (informal tasks pending completion) to FIXME's (something bad or suspicious that needs cleanup, usually before a release). To me, the style guide's p17 simply emphasizes this distinction, even if in a potentially confusing way.

[larskotthoff]

@khotilov Could you please disable the TODO lintr as suggested so we can see if the build succeeds then?

[khotilov]

@larskotthoff The build has passed.

[larskotthoff]

Thanks! Merging.