when using tablecloth, how to select rows in case my predicate needs the current row and a previous row? (eg I'd like to select rows based on today's temperature and yesterday's temperature). Current ideas (A) create an "index" column and access the previous row using index-1 (B) create a "delayed" version of the column I'd like to access from the previous row (C) somehow pass the last 2 rows into the tc/select-rows fn? Currently I like (A) the best, but I guess some of you met this problem before..