What is the origin of numeric dates starting with 6? - r

Question

I have dates as numeric, all starting with digit 6, I know that x date is between startDate and endDate.
Example data:
#dput(df1)
df1 <- structure(list(
startDate = structure(c(9748, 11474, 12204, 12204), class = "Date"),
endDate = structure(c(16645, 16535, 13376, 15863), class = "Date"),
x = c(63719L, 63622L, 60448L, 62940L)),
row.names = c(NA, -4L), class = "data.frame")
?as.Date suggests many origins, none works:
as.Date(63719, origin = "1900-01-01")
# [1] "2074-06-16"
as.Date(63719, origin = "1899-12-30")
# [1] "2074-06-14"
as.Date(63719, origin = "1904-01-01")
# [1] "2078-06-15"
as.Date(63719, origin = "1970-01-01")
# [1] "2144-06-16"
Any ideas?

Answer 1

The origin could be MUMPS origin date "1840-12-31", the reason for this date is explained in MUMPS Language faq:
27. "What happened in 1841?"
When I decided on specifications for the date routine, I remembered reading
of the oldest (one of the oldest?) U.S. citizen, a Civil War veteran, who
was 121 years old at the time. Since I wanted to be able to represent dates
in a Julian-type form so that age could be easily calculated and to be able
to represent any birth date in the numeric range selected, I decided that a
starting date in the early 1840s would be 'safe.' Since my algorithm worked
most logically when every fourth year was a leap year, the first year was
taken as 1841. The zero point was then December 30, 1840...
That's the origin of December 31, 1840 or January 1, 1841. I wasn't party
to the MDC negotiations, but I did explain the logic of my choice to members
of the Committee.
Wikipedia System time:
Language/Application Function or variable Resolution Epoch or range
MUMPS $H (short for $HOROLOG) 1 s 31 December 1840
Let's test:
df1$xClean <- as.Date(df1$x, origin = "1840-12-31")
df1$xClean > df1$startDate & df1$xClean < df1$endDate
# [1] TRUE TRUE TRUE TRUE
Note: Thanks to #Frank for pointing me to this blogpost which led me to original MUMPS faq. I posted self-answer Q&A for reference, as searching SO and Google didn't yield much.

Answer 2

You found already an answer, but for the fun of it, here a code snippet to automatize this:
library(rvest)
library(tidyverse)
library(magrittr)
df1 <- structure(list(
startDate = structure(c(9748, 11474, 12204, 12204), class = "Date"),
endDate = structure(c(16645, 16535, 13376, 15863), class = "Date"),
x = c(63719L, 63622L, 60448L, 62940L)),
row.names = c(NA, -4L), class = "data.frame")
epochs <- read_html("https://en.wikipedia.org/wiki/Epoch_(computing)") %>%
html_nodes(xpath = '//*[#id="mw-content-text"]/div/table') %>%
html_table() %>%
extract2(1) %>%
set_names(c("epoch", "users", "rationale")) %>%
mutate(epoch_date = parse_date(epoch, "%B %d, %Y", locale = locale("en"))) %>%
filter(!is.na(epoch_date))
potential_origins <- map_lgl(epochs$epoch_date,
function(origin) {
d <- as.Date(df1$x, origin = origin)
all(d >= df1$startDate & d <= df1$endDate)
})
epochs$users[potential_origins]
# [1] "MUMPS programming language"