nearest neighbors rule

Today, in (he claims) twenty minutes, inspired by our K-nearest-neighbors frenzy, Fadely built a nearest-neighbor data-driven photometric redshift system and it seems to work competitively straight out of the box. That led to an afternoon of nearest-neighbor hacking. I worked on expressing my issues about making KNN heteroskedastic (that is, switching to a weighted chi-squared definition of neighbor). Fadely and I pair-coded a tweak to our KNN detector calibration system, in which we don't use the neighbors naively, but rather use them to build a more complex model of the neighboring data space. Oh, there are whole careers that could be built on KNN methods!