時間の差を計算するときのはまりメモ
Rは２時点間の差によしなに単位をつけてくれる。
time0 <- ymd_hms("2018-11-11 00:00:00")
time1 <- ymd_hms("2018-11-11 11:11:11")
time2 <- ymd_hms("2018-12-31 23:59:59")
time1 - time0## Time difference of 11.18639 hourstime2 - time0## Time difference of 50.99999 days処理開始時刻と測定時刻をログしたhourスケールの実験exp_hourとdayスケールの実験exp_dayがある。
exp_hour <- tibble(init = time0, time = time1, dif = time - init)
exp_day <- tibble(init = time0, time = time2, dif = time - init)これをwrite_csv -> read_csvとするとdouble型に落ちて、実験間で単位に齟齬が生じる。
temp_file1 <- tempfile()
temp_file2 <- tempfile()
write_csv(exp_hour, path = temp_file1)
write_csv(exp_day, path = temp_file2)
exp_hour2 <- read_csv(temp_file1)
exp_day2 <- read_csv(temp_file2)
exp_hour2$dif## [1] 11.18639exp_day2$dif## [1] 50.99999実用的には、
as.numeric(units = "hours")で単位を指定するlubridateのduration系関数 (dhoursなど) で割って単位変換する
round(50.9999) * 24## [1] 1224exp_day %>% transmute(dif = as.numeric(dif, units = "hours")) %$% dif## [1] 1224exp_day %>% transmute(dif = dif / dhours(1)) %$% dif## [1] 1224ついでに、単位の異なる時間差をまとめて扱う場合、差をとる順序によって結果が変わってくる。
(exp_hour %<>% select(-dif))## # A tibble: 1 x 2
## init time
## <dttm> <dttm>
## 1 2018-11-11 00:00:00 2018-11-11 11:11:11(exp_day %<>% select(-dif))## # A tibble: 1 x 2
## init time
## <dttm> <dttm>
## 1 2018-11-11 00:00:00 2018-12-31 23:59:59# さきに差を計算
sub_before <-
bind_rows(
exp_hour %>% transmute(dif = time - init),
exp_day %>% transmute(dif = time - init)
)
sub_before## # A tibble: 2 x 1
## dif
## <time>
## 1 " 40271 secs"
## 2 4406399 secs# あとで差を計算
sub_after <-
bind_rows(exp_hour, exp_day) %>%
transmute(dif = time - init)
sub_after## # A tibble: 2 x 1
## dif
## <time>
## 1 " 11.18639 hours"
## 2 1223.99972 hoursmutateでは生成される列内で最小の単位に統一されるのに対し、cやbind_rowsでつなげると任意の単位の組み合わせからsecあるいはday単位のいずれかに換算されるのが原因。
dif_hour = ymd_hms("2018-11-11 06:00:00") - ymd_hms("2018-11-11 00:00:00")
dif_week = ymd_hms("2018-11-18 01:00:00") - ymd_hms("2018-11-11 00:00:00")
dif_month = ymd_hms("2018-12-11 01:00:00") - ymd_hms("2018-11-11 00:00:00")
dif_year = ymd_hms("2019-11-11 01:00:0") - ymd_hms("2018-11-11 00:00:00")
attributes(c(dif_hour, dif_week))$units## [1] "secs"attributes(c(dif_hour, dif_month))$units## [1] "secs"attributes(c(dif_hour, dif_year))$units## [1] "secs"attributes(c(dif_week, dif_month))$units## [1] "days"attributes(c(dif_week, dif_year))$units## [1] "days"attributes(c(dif_month, dif_year))$units## [1] "days"Session information
devtools::session_info()## setting value
## version R version 3.5.0 (2018-04-23)
## system x86_64, darwin15.6.0
## ui X11
## language (EN)
## collate en_US.UTF-8
## tz Australia/Sydney
## date 2018-11-13
##
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## assertthat 0.2.0 2017-04-11 CRAN (R 3.5.0)
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