Write plot function for mixed parameters about mlrmbo HOT 5 CLOSED

Started to work on this.

from mlrmbo.

Returning list of plots (as usual). Each plot contains of multiple facets: one facet for each level of the discrete or logical parameter.

from mlrmbo.

1. I have added example ex_mixed.R

2. Do we have a unit test for the plot? If not, add.

3. I want to discuss the plot and will keep this open til then.

from mlrmbo.

ad 1) Good.
ad 2) I am going to add a test soon.
ad 3) You said there are some things you dislike concerning the plots. Tell me more.

There are some things I am unsure about how to solve them in the best way:

• should display y and yhat in the same plot?
• standard error is missing as it exists in the 1d numeric case
• should we avoid using facets and display all functions in one plot using different line types? For example all infill crit curves in one plot? This might become very confusing if the number of factor levels of the discrete parameter is 3 or greater.

from mlrmbo.

Done. True objective function and model are now displayed within the same ggplot. Standard error ribbons are drawn as well, if standard error estimation is supported by learner and argument densregion is true.

from mlrmbo.