Time estimation in advance and progress bar

[PhilippPro]

Would be cool to have a time estimation in advance after choosing a learner and a progress bar, so you see how long it still takes to train/benchmark your model.

[larskotthoff]

I'm happy to look at any prototypes, but I think that this would be wildly inaccurate.

[berndbischl]

if you run a 10 fold CV you can estimate after the first iter, how long the rest might take.
but this seems more like an issue for mlr to display a progress bar here?
(as an option)