NickQiZhu/dc.js — pull request #298 by gordonwoodhull (2013-09-23 06:08:15+00:00)
Title: in flattenStacks, use a set to test belonging of ordinal Xs

the previous solution in PR #251 was still using relational
operators to test whether points' x coordinates were in the domain

this is not correct for ordinal coordinates, which don't have to be
ordered by the key (the domain specifies the order, not the
relational operators)