Data.table: 关键突破`by`功能

我不完全确定是什么导致了这种情况，所以这是我能找到的最小的 WE

library(data.table) # Tested on v 1.9.7
dt <-  data.table( origin = c("A", "A", "A", "A", "A", "A", "B", "B", "A", "A", "C", "C", "B", "B", "B", "B", "B", "C", "C", "B", "A", "C", "C", "C", "C", "C", "A", "A", "C", "C", "B", "B"),
                   destination = c("A", "A", "A", "A", "B", "B", "A", "A", "C", "C", "A", "A", "B", "B", "B", "C", "C", "B", "B", "A", "B", "C", "C", "C", "A", "A", "C", "C", "B", "B", "C", "C"),
                   points_in_dest = c(5, 5, 5, 5, 4, 4, 5, 5, 3, 3, 5, 5, 4, 4, 4, 3, 3, 4, 4, 5, 4, 3, 3, 3, 5,5, 3, 3, 4, 4, 3, 3),
                   depart_time = c(7, 8, 16, 18, 7, 8, 16, 18, 7, 8, 16, 18, 7, 8, 16, 7, 8, 16, 18, 8, 16, 7, 8, 18, 7, 8, 16, 18, 7, 8, 16, 18),   
                   travel_time = c(0, 0, 0, 0, 70, 10, 70, 10, 10, 10, 70, 70, 0, 0, 0, 70, 10, 10, 70, 70, 10, 0, 0, 0, 10, 70, 10, 70, 10, 70, 70, 10) )

dt[ depart_time<=8  & travel_time < 60, condition1 := TRUE]
dt[ depart_time>=16 & travel_time < 60, condition2 := TRUE] 

setkey(dt, origin, destination)
res <- unique(dt[(condition1)])[unique(dt[(condition2)]), 
                                on = c(destination = "origin", origin = "destination"), 
                                nomatch = 0L]
res[, .(points = sum(points_in_dest)),  keyby = origin]
#    origin points
#1:      A      5
#2:      A      4
#3:      B      4
#4:      B      3
#5:      C      5
#6:      C      4
#7:      C      3

如您所见， by未按预期工作，所有行均已返回。 这显然是一个键控问题，因为以下解决了这个问题

setattr(res, "sorted", NULL)
res[, .(points = sum(points_in_dest)), keyby = origin]
#    origin points
#1:      A      9
#2:      B      7
#3:      C     12

或者，或者将origin预先分类为一个因子

res[, .(points = sum(points_in_dest)), keyby = factor(origin)]
#    factor points
#1:      A      9
#2:      B      7
#3:      C     12

这取自这个 SO 问题http://stackoverflow.com/questions/37239649/aggregate-data-table-based-on-condition-in-another-row