On 22/06/2018 9:55 AM, Rui Barradas wrote:
Hello,
This just came up in SO, sessionInfo() at the end.
https://stackoverflow.com/questions/50988018/seeking-explanation-for-as-date-function-in-r?noredirect=1#comment88971055_50988018
# example 1
# not even the month is right
as.Date(x = 1, format = '%j', origin= '2015-01-01')
#[1] "2018-07-21"
Since x is numeric, it is added to the origin date. But the origin date
is a character, so it is converted to a date using format. The %j
format says "day of year"; since you didn't give a year, that is assumed
to be the current year, 2018. %j only uses the 1st 3 digits that it
finds, so the origin is taken to be day 201 of 2018. Add 1, you get
July 21.
# example 2a
# nonsense output
as.Date(x = 1, origin= '2015-01-01')
#[1] "2015-01-02"
Since no format is given, the origin is found using the default
conversion, which gives what you'd expect. Then we add one day.
# example 2a
# nonsense output, see example 6 below
as.Date(x = 1, origin = as.Date('2015-01-01'))
#[1] "2015-01-02"
Same as above. Same result, hurray!
# example 3
# I know that the method as.Date.numeric doesn't have
# argument 'format' but does have the dots argument.
# The format is passed on to strptime so maybe the problem is there.
as.Date(x = 1, format = '%j', origin= as.Date('2015-01-01'))
#[1] "2015-01-02"
There's no problem here. The format is ignored for numeric x and date
object origin. This is the same as 2a.
# example 4
# Wrong, documented.
# origin should be automatically coerced to class 'Date'
# This is documented to behave like example 6 below
as.Date(x = '1',format = '%j', origin= '2015-01-01')
#[1] "2018-01-01"
origin is ignored for character x. That is day 1 of the default year.
# example 5
# right, documented. x of class 'character' needs argument 'format'
as.Date(x = '1', origin= '2015-01-01')
#Error in charToDate(x) :
# string de caracteres não é um formato padrão não ambíguo
There's no default conversion for '1'.
# example 6
# the safe way, the only one that outputs the right date
as.Date(x = '1', format = '%j', origin= as.Date('2015-01-01'))
#[1] "2018-01-01"
origin is ignored again, so this is the same as number 4.
Duncan Murdoch
sessionInfo()
R version 3.4.4 (2018-03-15)
Platform: x86_64-pc-linux-gnu (64-bit)
Running under: Ubuntu 16.04.4 LTS
Matrix products: default
BLAS: /usr/lib/libblas/libblas.so.3.6.0
LAPACK: /usr/lib/lapack/liblapack.so.3.6.0
locale:
[1] LC_CTYPE=pt_PT.UTF-8 LC_NUMERIC=C
[3] LC_TIME=pt_PT.UTF-8LC_COLLATE=pt_PT.UTF-8
[5] LC_MONETARY=pt_PT.UTF-8LC_MESSAGES=pt_PT.UTF-8
[7] LC_PAPER=pt_PT.UTF-8 LC_NAME=C
[9] LC_ADDRESS=C LC_TELEPHONE=C
[11] LC_MEASUREMENT=pt_PT.UTF-8 LC_IDENTIFICATION=C
attached base packages:
[1] stats graphics grDevices utils datasets methods
[7] base
loaded via a namespace (and not attached):
[1] compiler_3.4.4 tools_3.4.4yaml_2.1.19
Or maybe I am missing something.
Thanks in advance,
Rui Barradas
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