[scikit-learn] How to not recalculate transformer in a Pipeline?

[Gael Varoquaux]

On Tue, Nov 29, 2016 at 10:13:00AM +1100, Joel Nothman wrote:
>    - We have had PRs #3951
>    <https://github.com/scikit-learn/scikit-learn/pull/3951> and #2086
>    <https://github.com/scikit-learn/scikit-learn/pull/2086> that build
>    memoising into Pipeline in one way or another.

Sorry, I had in mind that this was discussed, but I hadn't realized that
they were PRs. I think that 3951 is a good start. I would have comments
on it, but maybe I should make them in the PR.

>    - Andy and I have previously discussed alternative ways to set
>    parameters to avoid indirection issues created by wrappers.

I feel that these approaches are much more invasive. The nice thing about
a memoized pipeline is that is a a fairly local change.

I'll comment on 3951 in terms of this specific realization, but we can
discuss here if we want to take it further.

Gaël