Tracking the S&P 500 using ETFs holdings

Misleading title. The author is just web scraping ETF holdings and running some analysis on it. ETFs are required to publish daily holdings, so there's no secret there.

The best way to track the sp500 is with an ETF.

Interesting subjects would be figuring out proxy baskets using, let's say 100 components of the sp500 or sector SPDRs to track the sp500.