hy-group-by

;; Let s <- [((6, 2018), 6.0), ((10, 2018), 6.0), ((6, 2018), 12.0)])
(list (group-by s first))
;; >> [((6, 2018), <itertools...), ((10, 2018), <itertools...)
;; if I try
(list (second (first (list (group-by s first)))))

; I expect the list of elements having (6, 2018) as first element of the tuple