Re: [R] changing the day of the week in dates format

From: Dave Evens <daveevens1_at_yahoo.co.uk>
Date: Sun, 15 May 2011 16:13:30 +0100 (BST)

Hi Adrian,

Many thanks for your reply.

Suppose I wanted to increment the date by a year - how would I account for things like leap years?

Would I just do
> mydaysx[select] <- mydaysx[select] + 365.25*24*60*60

Regards,Dave



From: Adrian Duffner <duffnera_at_googlemail.com>

Cc: "r-help_at_r-project.org" <r-help_at_r-project.org> Sent: Sunday, 15 May 2011, 14:21
Subject: Re: [R] changing the day of the week in dates format

Hi Dave,

your problem is that you are working with a S3 class, what is mainly a list with naming convention. Hence it is possible to change just one entry of the list, but it is nearly never recommendable.

So a slight change to your code should provide you the required output:
> mydaysx[select] <- mydaysx[select] + 2*24*60*60
> select <- mydaysx$wday==6
> sum(select)
[1] 0

In this case not only the entry $mday of the list is changed, but the whole object is updated.

Cheers
Adrian

Am 14.05.2011 20:44, schrieb Dave Evens:
> Dear all,
>
> I have a question related to the POSIXlt function in R.
>
> I have a set of dates and times, for exmaple:
>
> startx<- as.POSIXct("2011-01-01 00:00:00")
> finx<- as.POSIXct("2011-12-31 00:00:00")
>
> daysx<- seq(startx, finx, by="24 hours")
>
> I
>  want to change the dates of all the days falling on a Saturday to the
> next working day (i.e. Monday). So I convert dates to POSIXlt
>
> mydaysx<- as.POSIXlt(daysx)
>
> Then I change select all the Saturday's and move them on to Monday
>
> select<- mydaysx$wday==6
> mydaysx$mday[select]<- mydaysx$mday[select] + 2
>
> However,
>  although all the new dates (i.e. mydaysx) are actual days of the year -
>  the $wday have not been updated and the $mdays have not all been
> corrected (i.e. those falling into the next month). So if I do
>
> select<- mydaysx$wday==6
>
> I still get the same set of days as before.
>
> Is there a way to do this?
>
> Thanks,
>
>     [[alternative HTML version deleted]]
>
> ______________________________________________
> 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
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>

        [[alternative HTML version deleted]]



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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. Received on Sun 15 May 2011 - 20:14:37 GMT

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