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 n?o ? um formato padr?o n?o amb?guo
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-8 LC_COLLATE=pt_PT.UTF-8
> [5] LC_MONETARY=pt_PT.UTF-8 LC_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_3.4.4 yaml_2.1.19
>
>
> Or maybe I am missing something.
>
> Thanks in advance,
>
> Rui Barradas
>
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