Notes and Tutorials on Economics, Data Science and Machine Learninghttps://www.arashfarahani.com/en-ushttps://www.arashfarahani.com/blog/post/backlit-3d-printed-world-map-design-notes/https://www.arashfarahani.com/blog/post/backlit-3d-printed-world-map-design-notes/Engineering a 2×3 ft 12-hexagon illuminated wall relief on a Bambu P2S: solving the floating-island dilemma with a 0.8 mm translucent cap, side-loaded N52 magnet tunnels, and M3 heat-set shear pins.Thu, 22 Oct 2026 00:00:00 GMT3D PrintingDigital FabricationHardwareArash Farahanihttps://www.arashfarahani.com/blog/post/keystonejs-work-around-to-heroku-mlab-mongodb-add-on-shutdown-1/https://www.arashfarahani.com/blog/post/keystonejs-work-around-to-heroku-mlab-mongodb-add-on-shutdown-1/Back in October, I got an email from Heroku saying that mLab MongoDB add-on is going away and I need to remove it from my Heroku App i.e. my personal website.  You can use the free Atlas MongoDB to keep your KeystoneJS or other Heroku apps up and running.Mon, 25 Jan 2021 00:00:00 GMTSoftwareTutorialsArash Farahanihttps://www.arashfarahani.com/blog/post/code-smells-clean-code/https://www.arashfarahani.com/blog/post/code-smells-clean-code/"Even bad code can function. But if code isn't clean, it can bring a development organization to its knees. Every year, countless hours and significant resources are lost because of poorly written code. But it doesn't have to be that way." (Source: [Clean Code]) Here's how to fix that!Tue, 26 May 2020 00:00:00 GMTData ScienceArash Farahanihttps://www.arashfarahani.com/blog/post/free-ssl-with-free-heroku-dynos-cloudflare-to-rescue/https://www.arashfarahani.com/blog/post/free-ssl-with-free-heroku-dynos-cloudflare-to-rescue/Free SSL with Free Heroku Dynos: Cloudflare to rescueMon, 25 May 2020 00:00:00 GMTTutorialsSoftwareArash Farahanihttps://www.arashfarahani.com/blog/post/deploying-keystone-js-to-heroku/https://www.arashfarahani.com/blog/post/deploying-keystone-js-to-heroku/This website is a KeystoneJS Content Management Service (CMS) App deployed to Heroku for free. Here's how you deploy to HerokuWed, 20 May 2020 00:00:00 GMTTutorialsArash Farahanihttps://www.arashfarahani.com/blog/post/top-100-data-science-interview-questions-work-in-progress/https://www.arashfarahani.com/blog/post/top-100-data-science-interview-questions-work-in-progress/Here are the first 30+ questions of the top 100 interview questions for data science. Their rest is a work in progress. Tue, 24 Mar 2020 00:00:00 GMTData ScienceStatisticsTutorialsArash Farahanihttps://www.arashfarahani.com/blog/post/playing-with-qlik-sense/https://www.arashfarahani.com/blog/post/playing-with-qlik-sense/I have been playing around with different interactive visualizations for a while. There are many options that I have tested including D3.js, Python bokeh and HoloViews, Tableau. Testing Qlik now. So far, I'm happy with it.Sat, 09 Feb 2019 00:00:00 GMTSoftwareData ScienceArash Farahanihttps://www.arashfarahani.com/blog/post/correcting-for-selection-bias/https://www.arashfarahani.com/blog/post/correcting-for-selection-bias/You are conducting a survey where participation is voluntary. Therefore, survey participants may be different from the population of interest. If you had many characteristics of the survey participants and the population, how would you infer population means from the sample? Tue, 06 Nov 2018 00:00:00 GMTStatisticsTutorialsArash Farahanihttps://www.arashfarahani.com/blog/post/staring-deep-into-your-ms-word-files/https://www.arashfarahani.com/blog/post/staring-deep-into-your-ms-word-files/I had many images in my 50-page word file, but compressing the images didn't reduce it's size down from 29 MBs. After searching and searching, I learned that I can open an MS Word document with Winrar. Tue, 03 Jul 2018 00:00:00 GMTTutorialsSoftwareArash Farahani