R help - Jul 2011 - How to convert number (matlab) to date

Hello

I am new to R and I need to convert some dates (numeric format by matlab) to
actual dates in R.

For instance,

Matlab -> 730456 -> >> datestr(730456)

ans 
02-Dec-1999

R - 
> library(zoo)
> as.Date(730456)
[1] "3969-12-03"

I don't not mind the output format but it needs to be right.


Many thanks

Ed

You need to specify the origin:

as.Date(730456, origin = "matlabs origin date")

HTH,

Josh

P.S. Alternately, you may be able to do something like:

## find R's numeric representation of 02-Dec-1999 and use the
difference from Matlabs to offset
MatLabROffset <- 730456 - as.numeric(as.Date("1999-12-02"))
as.Date(730456 - MatLabROffset)


On Sat, Jul 16, 2011 at 8:50 PM, Eduardo M. A. M. Mendes
<emammendes at gmail.com> wrote:
> Hello
>
> I am new to R and I need to convert some dates (numeric format by matlab)
to actual dates in R.
>
> For instance,
>
> Matlab -> 730456 -> >> datestr(730456)
>
> ans >
> 02-Dec-1999
>
> R -
>
>> library(zoo)
>> as.Date(730456)
> [1] "3969-12-03"
>
> I don't not mind the output format but it needs to be right.
>
>
> Many thanks
>
> Ed
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>


-- 
Joshua Wiley
Ph.D. Student, Health Psychology
University of California, Los Angeles
https://joshuawiley.com/

Hi:

The default time origin in R is '1970-01-01'.

as.Date('1999-12-02') - as.Date('1970-01-01')
Time difference of 10927 days

Therefore, the difference in days between Matlab's and R's origins is
10927 - 730456
[1] -719529

as.Date(-719529, origin = '1970-01-01')
[1] "000/-12-31"

If we try this as an origin,
> as.Date(730456, origin = "000/-12-31")
Error in charToDate(x) :
  character string is not in a standard unambiguous format

Checking the as.Date() help page, we find the line
"Years before 1CE (aka 1AD) will probably not be handled correctly."
However, if we add a day,

as.Date(730456, origin = '0000-01-01')
[1] "1999-12-03"
which is one day later. So it appears that by subtracting 1 from the
Matlab date and using origin '0000-01-01' should work.

Matlab2Rdate <- function(val) as.Date(val - 1, origin =
'0000-01-01')
> Matlab2Rdate(730456)
[1] "1999-12-02"

HTH,
Dennis


On Sat, Jul 16, 2011 at 8:50 PM, Eduardo M. A. M. Mendes
<emammendes at gmail.com> wrote:
> Hello
>
> I am new to R and I need to convert some dates (numeric format by matlab)
to actual dates in R.
>
> For instance,
>
> Matlab -> 730456 -> >> datestr(730456)
>
> ans >
> 02-Dec-1999
>
> R -
>
>> library(zoo)
>> as.Date(730456)
> [1] "3969-12-03"
>
> I don't not mind the output format but it needs to be right.
>
>
> Many thanks
>
> Ed
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

On Sat, Jul 16, 2011 at 11:50 PM, Eduardo M. A. M. Mendes
<emammendes at gmail.com> wrote:
> Hello
>
> I am new to R and I need to convert some dates (numeric format by matlab)
to actual dates in R.
>
> For instance,
>
> Matlab -> 730456 -> >> datestr(730456)
>
> ans >
> 02-Dec-1999
>
Set the origin to Matlab's origin like this.  Be sure you are using
the indicated version of zoo or later:
> library(zoo)
> packageVersion("zoo")
[1] ?1.7.1?
> as.Date(730456, origin = "0000-00-00")
[1] "1999-12-02"


-- 
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