Lubridate间隔在dplyr join()中丢失，但在基础merge()中丢失：
library(dplyr)
library(lubridate)
(foo <-
tibble(
start = seq(as.Date("2016-01-01"), by = 1, length.out = 2),
end = seq(as.Date("2016-01-02"), by = 2, length.out = 2)
) %>%
transmute(itv = interval(start, end), dummy = 1))
# # A tibble: 2 × 2
# itv dummy
# <S4: Interval> <dbl>
# 1 2016-01-01 UTC--2016-01-02 UTC 1
# 2 2016-01-02 UTC--2016-01-04 UTC 1
NA来自哪里？
foo %>%
inner_join(., ., by = "dummy")
# A tibble: 4 × 3
# itv.x dummy itv.y
# <S4: Interval> <dbl> <S4: Interval>
# 1 2016-01-01 UTC--2016-01-02 UTC 1 2016-01-01 UTC--2016-01-02 UTC
# 2 2016-01-02 UTC--2016-01-03 UTC 1 2016-01-02 UTC--2016-01-04 UTC
# 3 NA--NA 1 NA--NA
# 4 NA--NA 1 NA--NA
基础merge()看起来很好：
foo %>%
merge(., ., by = "dummy")
# dummy itv.x itv.y
# 1 1 2016-01-01 UTC--2016-01-02 UTC 2016-01-01 UTC--2016-01-02 UTC
# 2 1 2016-01-01 UTC--2016-01-02 UTC 2016-01-02 UTC--2016-01-04 UTC
# 3 1 2016-01-02 UTC--2016-01-04 UTC 2016-01-01 UTC--2016-01-02 UTC
# 4 1 2016-01-02 UTC--2016-01-04 UTC 2016-01-02 UTC--2016-01-04 UTC
这可能是个错误吗？或者只是我对Interval S4课程做错了什么？
sessionInfo()
# R version 3.3.2 (2016-10-31)
# Platform: x86_64-pc-linux-gnu (64-bit)
# Running under: Linux Mint 18
#
# locale:
# [1] LC_CTYPE=fr_FR.UTF-8 LC_NUMERIC=C LC_TIME=fr_FR.UTF-8 LC_COLLATE=fr_FR.UTF-8 LC_MONETARY=fr_FR.UTF-8
# [6] LC_MESSAGES=fr_FR.UTF-8 LC_PAPER=fr_FR.UTF-8 LC_NAME=C LC_ADDRESS=C LC_TELEPHONE=C
# [11] LC_MEASUREMENT=fr_FR.UTF-8 LC_IDENTIFICATION=C
#
# attached base packages:
# [1] stats graphics grDevices utils datasets methods base
#
# other attached packages:
# [1] lubridate_1.6.0 dplyr_0.5.0
#
# loaded via a namespace (and not attached):
# [1] magrittr_1.5 R6_2.2.0 assertthat_0.1 DBI_0.5-1 tools_3.3.2 tibble_1.2 Rcpp_0.12.9 stringi_1.1.2 stringr_1.1.0