Hey, if you’re hunting for the sweet spot between compression and speed, give CSR or CSC a spin – they’re the OGs for row‑major or column‑major sweeps. If you can afford a bit of overhead, COO’s great for random inserts, then pack it into a compressed block format like BCSR or ELLPACK when you hit regular patterns. For really crazy sparsity, look at sparse hash tables or bit‑packed indices – they keep cache lines tight but can slow a single lookup a tad. Bottom line: keep the data layout friendly to your access pattern; a small cache‑friendly chunk often beats a monolithic compressed blob. Happy hacking!