# [R] Time data

Gabor Grothendieck ggrothendieck at gmail.com
Tue Dec 20 15:29:59 CET 2005

```On 12/20/05, Marc Bernard <bernarduse1 at yahoo.fr> wrote:
> Dear All, I wonder how to compute the age from the date of birth and the date of examination. Suppose that have the following data:
>
>  df <- as.data.frame(rbind(c(1,"10/08/1950","15/03/1998"), c(1,"10/08/1950","20/07/1998"), c(1,"10/08/1950","23/10/1998")))
>
>  names(df) <- c("ID", "date_birth", "date_exam")
>
>  where:
>  date_birth: is the date of birth
>  date_exam: date of examination
>
>  I used the following program to compute the value of the age  :
>

First ensure that df stores its dates using "Date" class in the first
place.  If your data is stored in the correct representation then
everything becomes easier subsequently:

fmt <- "%d/%m/%Y"
df[,2] <- as.Date(df[,2], fmt)
df[,3] <- as.Date(df[,3], fmt)

# converting them to numeric gives the number of days since
# the Epoch and one can just subtact those:

(as.numeric(df\$date_exam) - as..numeric(df\$date_birth)) / 365

>  difftime(strptime(as.character(df\$date_exam), '%d/%m/%Y'), strptime(as.character(df\$date_birth), '%d/%m/%Y'))/365.25
>
>  which gives me as an output:
>
> > Time differences of 47.59491, 47.94251, 48.20260 days
>
>  theses values are actually the 3 ages (but
>
>  My questions are:
>
>  1- Why in the output it says "days" instead of "years")
>
>  2- How can I obtain the output as a numeric vector, without the statement "Time difference of ....". This is in order to use it in my calculations.
>
>  3- Is there a way quicker and less redondant  to compute the age form the date_birth and date_exam?
>
>  Thanks a lot,
>
>  Bernard,
>
>
>
> ---------------------------------
>
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>
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