data.table non-equi joins

library(data.table)
# data generation
numBus <- 20L
departTimeSpan <- "20 mins"
data1 <- data.table(busNo = 1L:numBus,
                    departTime = seq.POSIXt(as.POSIXct("1990-01-01 05:50:00"),
                                            by = departTimeSpan, length.out = numBus))
## data1
#     busNo          departTime
#  1:     1 1990-01-01 05:50:00
#  2:     2 1990-01-01 06:10:00
#  3:     3 1990-01-01 06:30:00
#  4:     4 1990-01-01 06:50:00
#  5:     5 1990-01-01 07:10:00
#  6:     6 1990-01-01 07:30:00
#  7:     7 1990-01-01 07:50:00
#  8:     8 1990-01-01 08:10:00
#  9:     9 1990-01-01 08:30:00
# 10:    10 1990-01-01 08:50:00
# 11:    11 1990-01-01 09:10:00
# 12:    12 1990-01-01 09:30:00
# 13:    13 1990-01-01 09:50:00
# 14:    14 1990-01-01 10:10:00
# 15:    15 1990-01-01 10:30:00
# 16:    16 1990-01-01 10:50:00
# 17:    17 1990-01-01 11:10:00
# 18:    18 1990-01-01 11:30:00
# 19:    19 1990-01-01 11:50:00
# 20:    20 1990-01-01 12:10:00

# 產生2015/10/01~2015/12/31中前後五分鐘的班次
dataCnt <- 5L
data2 <- data.table(departTime = sample(data1$departTime, dataCnt, TRUE) +
                      as.difftime(sample(9404:9495, dataCnt, TRUE), units = "days") +
                      as.difftime(sample(-300:300, dataCnt, TRUE), units = "secs"))
#             departTime
# 1: 2015-11-25 08:49:53
# 2: 2015-10-27 09:47:25
# 3: 2015-11-02 10:27:39
# 4: 2015-10-18 08:11:40
# 5: 2015-12-02 09:11:13

## method 1
# find the departure time range
diffTime5mins <- as.difftime(5, units = "mins")
data1[ , start := departTime - diffTime5mins]
data1[ , end := departTime + diffTime5mins]
setkey(data1, start, end)

# align time to 1990/01/01
data2[ , start := departTime - floor(departTime - as.POSIXct("1990-01-01 00:00:00"))]
data2[ , end := start]

# use foverlaps to find the busNo
foverlaps(data2, data1)[ , .(i.departTime, busNo)]
#           i.departTime busNo
# 1: 2015-11-25 08:49:53    10
# 2: 2015-10-27 09:47:25    13
# 3: 2015-11-02 10:27:39    15
# 4: 2015-10-18 08:11:40     8
# 5: 2015-12-02 09:11:13    11

## method 2
# find the departure time range
diffTime5mins <- as.difftime(5, units = "mins")
data1[ , start := departTime - diffTime5mins]
data1[ , end := departTime + diffTime5mins]
setkey(data1, start, end)
# align time to 1990/01/01
data2[ , departTimeAlign := departTime - floor(departTime - as.POSIXct("1990-01-01 00:00:00"))]
# use Non-equi joins
data2[data1, on = .(departTimeAlign >= start, departTimeAlign <= end), nomatch = 0][ , .(departTime, busNo)]
#             departTime busNo
# 1: 2015-10-18 08:11:40     8
# 2: 2015-11-25 08:49:53    10
# 3: 2015-12-02 09:11:13    11
# 4: 2015-10-27 09:47:25    13
# 5: 2015-11-02 10:27:39    15