R help - Sep 2007 - Calculate difference between dates in years

Hello,

I would like to be able to calculate the age of someone at a particular
date.  Both dates are date objects.  Here is what I have come up with:

floor(as.numeric(sampleInfo$Date.of.DIAGNOSIS-sampleInfo$Date.of.birth)/365.25)

Is this the best approach? or is there an inbuilt function?  I have
looked at difftime but that does not seem to allow output in years.

Many thanks

Dan

-- 
**************************************************************
Daniel Brewer, Ph.D.
Institute of Cancer Research
Email: daniel.brewer at icr.ac.uk
**************************************************************

The Institute of Cancer Research: Royal Cancer Hospital, a charitable Company
Limited by Guarantee, Registered in England under Company No. 534147 with its
Registered Office at 123 Old Brompton Road, London SW7 3RP.

This e-mail message is confidential and for use by the addre...{{dropped}}

look at the as.Date function

e.g.

as.Date("2007-04-21")- as.Date("2000-04-21")


also look at the chron library. 

Regards

Wayne


-----Original Message-----
From: r-help-bounces at r-project.org
[mailto:r-help-bounces at r-project.org]On Behalf Of Daniel Brewer
Sent: 24 September 2007 11:23
To: r-help at stat.math.ethz.ch
Subject: [R] Calculate difference between dates in years


Hello,

I would like to be able to calculate the age of someone at a particular
date.  Both dates are date objects.  Here is what I have come up with:

floor(as.numeric(sampleInfo$Date.of.DIAGNOSIS-sampleInfo$Date.of.birth)/365.25)

Is this the best approach? or is there an inbuilt function?  I have
looked at difftime but that does not seem to allow output in years.

Many thanks

Dan

-- 
**************************************************************
Daniel Brewer, Ph.D.
Institute of Cancer Research
Email: daniel.brewer at icr.ac.uk
**************************************************************

The Institute of Cancer Research: Royal Cancer Hospital, a charitable Company
Limited by Guarantee, Registered in England under Company No. 534147 with its
Registered Office at 123 Old Brompton Road, London SW7 3RP.

This e-mail message is confidential and for use by the =\ ad...{{dropped}}

Daniel Brewer wrote:
> 
> I would like to be able to calculate the age of someone at a particular
> date.  Both dates are date objects.  Here is what I have come up with:
> 
> floor(as.numeric(sampleInfo$Date.of.DIAGNOSIS-
> sampleInfo$Date.of.birth)/365.25)
> 
> Is this the best approach?
>
No - leap years and such. You know that there are _not_
365.25 days in one year, don't you?

floor(as.numeric(as.Date("2100-02-28") -
as.Date("1900-02-28"))/365.25)
# 199, should be 200

A less extreme counter-example:

floor(as.numeric(as.Date("2008-02-28") -
as.Date("2007-02-28"))/365.25)
# 0, should be 1

Alberto Monteiro (purely destructive - sorry)