Hi Stefano,
What about this?
df$months<-format(df$data_POSIX,"%Y-%m")
snow_means<-by(df$value,df$months,mean)
Jim
On Mon, Sep 14, 2020 at 8:19 PM Stefano Sofia
<stefano.so...@regione.marche.it> wrote:
>
> Dear R-list users,
> I know that this is a trivial question, but I already wasted quite a large
> amount of time on that.
> I have a data frame with daily data of snow fall. I need to evaluate the
> monthly mean for each month and each year in the data frame.
> Could you help me to find an eficient way for these calculations?
>
> Thank you for your help
> Stefano
>
> Here a reproducibile code:
>
> first_day_1 <- as.POSIXct("2019-01-19-00-00", format="%Y-%m-%d-%H-%M")
> last_day_1 <- as.POSIXct("2019-03-20-00-00", format="%Y-%m-%d-%H-%M")
> df1 <- data.frame(data_POSIX=seq(first_day_1, last_day_1, by="1 days"))
> df1$value <- runif(nrow(df1), 0, 10)
>
>
> first_day_2 <- as.POSIXct("2020-02-19-00-00", format="%Y-%m-%d-%H-%M")
> last_day_2 <- as.POSIXct("2020-04-20-00-00", format="%Y-%m-%d-%H-%M")
> df2 <- data.frame(data_POSIX=seq(first_day_2, last_day_2, by="1 days"))
> df2$value <- runif(nrow(df2), 0, 10)
>
> df <- rbind(df1, df2)
>
>
>
>
>
> (oo)
> --oOO--( )--OOo----------------
> Stefano Sofia PhD
> Civil Protection - Marche Region
> Meteo Section
> Snow Section
> Via del Colle Ameno 5
> 60126 Torrette di Ancona, Ancona
> Uff: 071 806 7743
> E-mail: stefano.so...@regione.marche.it
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