[R] unable to subtract dates in R

[arun]

Hi,

It is a bit difficult to give suggestions when there are no example datasets.
Have you checked whether both belong to "Date" class?

You could use, 
difftime(intakeDS$DOB, intakeDS$IntakeDate_d,units="days")
to get the difference between dates
A.K.




----- Original Message -----
From: William Mabe <billmabe at gmail.com>
To: r-help at r-project.org
Cc: 
Sent: Wednesday, July 11, 2012 6:20 PM
Subject: [R] unable to subtract dates in R

Hi,

I wanted to calculate the age of people in my dataset by subtracting the
individual's date of birth from their intake into a program.

After several hours, searches of help archives, and the downloading of
lubiridate, I have had no luck with this.

Below is the code I used.

> intakeDS$DOB <- as.character(intakeDS$DOB)

> intakeDS$DOB <- as.Date(intakeDS$DOB, "%Y%m%d")

>

> # Make IntakeDate a date variable, by first converting it from numeric to
character then from character to date

> #intakeDS$IntakeDate <- as.character(intakeDS$IntakeDate)

> intakeDS$IntakeDate_d <- as.Date(intakeDS$IntakeDate_c, "%Y%m%d")

>

> intakeDS$intake_age <- intakeDS$DOB - intakeDS$IntakeDate_d

> intakeDS$intake_age

Time differences in days

  [1] NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA
NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA
NA NA NA NA NA NA NA NA NA NA NA NA

[61] NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA
NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA
NA NA NA NA NA NA NA NA NA NA NA NA

[121] NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA
NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA
NA NA NA NA NA NA NA NA NA NA NA NA

[181] NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA
NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA
NA NA NA NA NA NA NA NA NA NA NA NA

[241] NA NA NA NA NA NA NA


I also downloaded the lubridate package and used the new_interval command
and that created a variable that showed the start date and the end date.
However, I was not able to subtract one date from the other to calculate an
age variable.


Any help would be greatly appreciated as this has been a pretty miserable
afternoon hacking away at this.


Thanks,

Bill

    [[alternative HTML version deleted]]

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