[R] calculating the number of days from dates

[Henrique Dallazuanna]

Try this:

dates <- read.csv("c:\\dates.csv",header=T)
dates[,1] <- as.Date(dates[,1], "%d/%m/%Y")
dates[,2] <- as.Date(dates[,2], "%d/%m/%Y")
transform(dates,
     Dif=V2-V1)

On 14/12/2007, Bob Green <bgreen at dyson.brisnet.org.au> wrote:
>
> Hello,
>
> I gather variants of this question have been asked previously. I have
> done some reading but only became more confused, as I suspect what I
> am trying to do is more basic than other applications.
>
> The following code readily calculates the difference in days between two dates:
>
>  newdays <- ISOdate(2005, 5,12) - ISOdate(2006, 12, 22)
>
> However, I wanted to be able to deduct the dates in one variable from
> the dates in another variable, resulting in a new variable - e.g the
> difference in days between the two dates. Below is a sample of my
> data. My questions:
>
> 1. I tried changing the data to dates via as.Date. Is this necessary
> or do I need to alter the date format itself, e.g to 12/12/78 or some
> other format?
> 2. I gather there are various packages as well as date formats.What
> is the most straight forward approach to calculate the difference
> between two dates, as below.
>
>
>  > dates <- read.csv("c:\\dates.csv",header=T)
>  > dates
>           v1         v2
> 1 12/12/1978 12/12/2005
> 2 23/01/1965 23/09/2001
> 3 24/12/2004 16/03/2007
> 4  3/03/2003  4/04/2004
> 5  8/11/2006  1/05/2007
>
>  > class(dates$v1)
> [1] "factor"
>  > class(dates$v2)
> [1] "factor"
>
>  > dates <- read.csv("c:\\dates.csv",header=T,
> as.Date(as.character(dates) "%d/%m/%Y"))
> Error: syntax error, unexpected STR_CONST, expecting ',' in "dates <-
> read.csv("c:\\dates.csv",header=T, as.Date(as.character(dates) "%d/%m/%Y""
>  >
>
> Any assistance is much appreciated,
>
> Bob
>
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-- 
Henrique Dallazuanna
Curitiba-Paraná-Brasil
25° 25' 40" S 49° 16' 22" O