So, this is the perfect example of what I am talking about. Getting something you can generously call a charting library isn’t that hard, getting something worth the time building on it’s own merits is. If you want to have a fun side project go for it. However, if the goal is to actually make charts it’s extremely unlikely that starting from scratch is a good idea.
And yet I still had a dev get pissed off by my offer to help with a charting problem. "Yeah, but was it D3?"
I'm generally an advocate for buy-before-build in software, but I don't trust the kind of dev who won't even acknowledge that the easy part of a problem is easy (or that true experience isn't framework specific).
A couple of months ago, a junior developer mentioned he'd need a library for a bar chart, and asked for directions how to use it in an Xcode project. It turned out to be easier to draw the chart with a few rectangles, and the developer had one of those great a-ha moments.