[R] aggregate function

[Gabor Grothendieck]

try this.  The first group of lines recreates your data frame, DF, and
the last line is the aggregate:


Input <- "Date            Time    z
2006-01-01      21:00   6,2
2006-01-01      22:00   5,7
2006-01-01      23:00   3,2
2006-01-02      00:00   7,8
2006-01-02      01:00   6,8
2006-01-02      02:00   5,6
2007-03-30      22:00   5,2
2007-03-30      23:00   8,3
2007-03-31      00:00   6,4
2007-03-31      01:00   7,4
"
DF <- read.table(textConnection(Input), header = TRUE, as.is = TRUE)
DF$z <- as.numeric(sub(",", ".", DF$z))
DF$Date <- as.Date(DF$Date)

aggregate(DF["z"], list(yearmon = format(DF$Date, "%Y-%m")), mean)



On 4/23/07, Michel Schnitz <michel.schnitz at web.de> wrote:
> Hello,
>
> is there a way to use the aggregate function to calculate monthly mean
> in case i have one row in data frame that holds the date like
> yyyy-mm-dd? i know that it works for daily means. i also like to do it
> for monthly and yearly means. maybe there is something like aggregate(x,
> list(Date[%m]), mean)?
> the data frame looks like:
>
> Date            Time    z
> 2006-01-01      21:00   6,2
> 2006-01-01      22:00   5,7
> 2006-01-01      23:00   3,2
> 2006-01-02      00:00   7,8
> 2006-01-02      01:00   6,8
> 2006-01-02      02:00   5,6
> .
> .
> .
> 2007-03-30      22:00   5,2
> 2007-03-30      23:00   8,3
> 2007-03-31      00:00   6,4
> 2007-03-31      01:00   7,4
>
> thanks for help!
> --
> Michél Schnitz
> michel.schnitz at web.de
>
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