Simplify some time-comsuming examples

[qinhanmin2014]

Some examples are time consuming. I think we should try to simplify them to make these examples more friendly to users and CI.
Examples > 60s (from https://circleci.com/gh/scikit-learn/scikit-learn/50704):

• plot_coin_segmentation.py: 4.6e+02 sec
• plot_iterative_imputer_variants_comparison.py: 1.9e+02 sec
• plot_rbm_logistic_classification.py: 1.5e+02 sec
• plot_pca_vs_fa_model_selection.py: 1.2e+02 sec
• plot_image_denoising.py: 1.1e+02 sec
• plot_digits_pipe.py: 80 sec
• plot_compare_reduction.py: 69 sec

See #13379 #12929

[vcGomez]

Hi! Could I give a try on this? That would be my first issue.

[qinhanmin2014]

Hi! Could I give a try on this? That would be my first issue.

Welcome to contribute :)

[vcGomez]

Thanks! :)

[jnothman]

@vbarroso, under ./build_tools/circle/build_doc.sh, download the full output as a file, and search for "computation time summary"

[Framartin]

I started to take a look at the examples/neural_networks/plot_rbm_logistic_classification.py example and I might start working on other mentioned ones. See #13648

[anestisdotpy]

Hello. Could I work on this? I have never contributed to open source before so I am a newbie.
Thanks in advance!

[thomasjpfan]

Hello. Could I work on this? I have never contributed to open source before so I am a newbie. ...

@anestisdotpy You are welcome to contribute! :)

[anestisdotpy]

@anestisdotpy You are welcome to contribute! :)

Thank you very much!

[sadepu1915]

@qinhanmin2014 do we have room to contribute on this ?

[qinhanmin2014]

@qinhanmin2014 do we have room to contribute on this ?

try to pick an example which do not have a PR.

[abhishek-jana]

@qinhanmin2014 I'm new to open source contribution. Can I contribute to this?

[rth]

@abhishek-jana Yes, definitely. Thanks!

[amueller]

@abhishek-jana sure, just pick on of the examples (say here which) and start working on it.

[abhishek-jana]

Thanks.

[abhishek-jana]

@abhishek-jana sure, just pick on of the examples (say here which) and start working on it.

I'll be looking into plot_compare_reduction.py thanks.

[Timsaur]

working on plot_digits_pipe.py

[qinhanmin2014]

I'm going to close this, according to the latest log https://circleci.com/gh/scikit-learn/scikit-learn/64630, no example takes more than 60s, only two examples take more than 30s (plot_face_recognition.py and plot_sgd_early_stopping.py), which seems acceptable.
Thanks everyone here.