r - 使用不等式表达式的内连接

Question

背景

(问题不是必需的，但阅读可能有用)

Rolling join on data.table with duplicate keys

Odd behaviour when joining with multiple conditions

数据

library(data.table)   ## using version 1.9.6
## arrival timetable
dt_arrive <- structure(list(txn_id = c(1L, 1L, 1L, 1L, 1L), place = c("place_a", 
"place_a", "place_a", "place_a", "place_a"), arrival_minutes = c(515, 
534, 547, 561, 581), journey_id = 1:5), .Names = c("txn_id", 
"place", "arrival_minutes", "journey_id"), class = c("data.table", 
"data.frame"), row.names = c(NA, -5L), sorted = c("txn_id", 
"place"))

## departure timetable
dt_depart <- structure(list(txn_id = c(1L, 1L, 1L, 1L), place = c("place_a", 
"place_a", "place_a", "place_a"), arrival_minutes = c(489, 507, 
519, 543), journey_id = 10:13), .Names = c("txn_id", "place", 
"arrival_minutes", "journey_id"), sorted = c("txn_id", "place"
), class = c("data.table", "data.frame"), row.names = c(NA, -4L
))

> dt_arrive
   txn_id   place arrival_minutes journey_id
1:      1 place_a             515          1
2:      1 place_a             534          2
3:      1 place_a             547          3
4:      1 place_a             561          4
5:      1 place_a             581          5

> dt_depart
   txn_id   place arrival_minutes journey_id
1:      1 place_a             489         10
2:      1 place_a             507         11
3:      1 place_a             519         12
4:      1 place_a             543         13

问题

我想加入 的到达和离开只有那些dt_depart$journey_id发生的 后 dt_arrive$journey_id在 arrival_minutes 方面(即 txn_id 和 place 上的内连接)

例如，我想要的输出是:

   txn_id   place journey_in_id journey_out_id journey_place_arrive journey_place_depart
      1     place_a          1             12                  515                  519
      1     place_a          1             13                  515                  543
      1     place_a          2             13                  534                  543

尝试

使用我构建的两个链接问题中的方法

setkey(dt_arrive, txn_id, place)
setkey(dt_depart, txn_id, place)

dt_join <- dt_arrive[dt_depart,
            {
              idx = (i.arrival_minutes > arrival_minutes)
              .(journey_in_id = journey_id[idx],
                journey_out_id = i.journey_id,
                journey_place_arrive = arrival_minutes[idx],
                journey_place_depart = i.arrival_minutes
              )
            },
            by=.EACHI]

但这给出了来自 dt_depart 的所有信息，所以包括 NA结果中的 s - 这表明“正确连接”:

   txn_id   place journey_in_id journey_out_id journey_place_arrive journey_place_depart
1:      1  place_a         NA             10                   NA                  489
2:      1  place_a         NA             11                   NA                  507
3:      1  place_a          1             12                  515                  519
4:      1  place_a          1             13                  515                  543
5:      1  place_a          2             13                  534                  543

我试过使用 nomatch=0强制它“内部连接”，但这没有用。

我可以用 complete.cases删除 NA行，但我想知道是否有办法在查询本身中做到这一点？

Answer 1

这是不聪明的方法:采用交叉/笛卡尔连接，然后过滤。

merge(dt_arrive, dt_depart, allow.cartesian=TRUE)[arrival_minutes.y > arrival_minutes.x]

#    txn_id   place arrival_minutes.x journey_id.x arrival_minutes.y journey_id.y
# 1:      1 place_a               515            1               519           12
# 2:      1 place_a               515            1               543           13
# 3:      1 place_a               534            2               543           13

通过采用笛卡尔连接，我们很可能会吃掉很多内存。