[R] add only the 1st of May with POSIXct

Wed May 29 08:01:25 CEST 2024

Thank you Rui for your code.

I basically understood all your suggestions.

I am using an old version of R (version 3.6.3, installed in a server I am not allowed to control), and the new pipe operator does not work.

I tried to run your code without the "|>" operator, but I get an error when I use apply.

Could you please expand your code without the pipe operator?

Thank you again for your help

Stefano

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Stefano Sofia PhD
Civil Protection - Marche Region - Italy
Meteo Section
Snow Section
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________________________________
Da: Rui Barradas <ruipbarradas using sapo.pt>
Inviato: martedì 28 maggio 2024 18:19
A: Stefano Sofia; r-help using R-project.org
Oggetto: Re: [R] add only the 1st of May with POSIXct

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Às 16:23 de 28/05/2024, Stefano Sofia escreveu:
> Dear R-list users,
>
>  From an initial and a final date I create a sequence of days using POSIXct.
>
> If this interval covers all or only in part the months from May to October, I need to get rid of the days from the 2nd of May to the 31st of October:
>
>
> a <- as.POSIXct("2002-11-01", format = "%Y-%m-%d", tz="Etc/GMT-1")
>
> b <- as.POSIXct("2004-06-01", format = "%Y-%m-%d", tz="Etc/GMT-1")
>
> mydf <- data.frame(data_POSIX=seq(as.POSIXct(paste(format(a, "%Y-%m-%d"), "09:00:00", sep=""), format="%Y-%m-%d %H:%M:%S", tz="Etc/GMT-1"), as.POSIXct(paste(format(b, "%Y-%m-%d"), "09:00:00", sep=""), format="%Y-%m-%d %H:%M:%S", tz="Etc/GMT-1"), by="1 day"))
>
>
> If I execute
>
> as.data.frame(mydf[format(mydf$data_POSIX,"%m") %in% c("11", "12", "01", "02", "03", "04"), ])
>
> the interval will be
>
> from 2002-11-01 09:00:00 to 2003-04-30 09:00:00
>
> and from 2003-11-01 09:00:00 to 2004-04-30 09:00:00
>
>
> but I need also 2003-05-01 09:00:00 and 2004-05-01 09:00:00
>
>
> How can I solve this problem?
>
>
> Thank you for your attention and your help
>
> Stefano
>
>
>
>           (oo)
> --oOO--( )--OOo--------------------------------------
> Stefano Sofia PhD
> Civil Protection - Marche Region - Italy
> Meteo Section
> Snow Section
> Via del Colle Ameno 5
> 60126 Torrette di Ancona, Ancona (AN)
> Uff: +39 071 806 7743
> E-mail: stefano.sofia using regione.marche.it
> ---Oo---------oO----------------------------------------
>
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Hello,

First of all, 'a' and 'b' are already objects of class "POSIXct", you
don't need to repeat the code creating them when creating mydf.

As for the question, see the code below.

a <- as.POSIXct("2002-11-01", format = "%Y-%m-%d", tz="Etc/GMT-1")
b <- as.POSIXct("2004-06-01", format = "%Y-%m-%d", tz="Etc/GMT-1")
mydf <- data.frame(data_POSIX = seq(a, b, by = "1 day"))

# get the years from the data
years <- format(c(a, b), "%Y") |> as.integer()
# this creates a sequence with all the years
years <- Reduce(`:`, years)

# coerce to "Date"
from <- ISOdate(years, 5L, 2L, tz = "Etc/GMT-1")
to <- ISOdate(years, 10L, 30L, tz = "Etc/GMT-1")

# this logical index keeps only the dates between May, 2nd and Nov 1st.
keep <- data.frame(from, to) |>
   apply(1L, \(x) x[1L] <= mydf$data_POSIX & mydf$data_POSIX <= x[2L]) |>
   rowSums() > 0L

mydf[keep, , drop = FALSE]

Hope this helps,

Rui Barradas

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