R help - Feb 2007 - How can I calculate conditional mean in a large dataset including date data

Dear R users,

I have a dataframe with two columns: first column is date data (e.g. 
1/1/2000 with character format: daily data from 1/1/1970 till 31/12/2003) 
and second column is temperature value. Now I'd like to calculate mean for 
each month in a year (i.e. May 2001, June 1997) and mean for each month in 
all of years. As the number of days in some months is different from others 
I could not write appreciate command for this. Therefore I would greatly 
appreciate if somebody can help me in this case

Thank you
Majid
--------------------------------------------------------------------------------
  Majid Iravani
  PhD Student
  Swiss Federal Research Institute WSL
  Research Group of Vegetation Ecology
  Z?rcherstrasse 111  CH-8903 Birmensdorf  Switzerland
  Phone: +41-1-739-2693
  Fax: +41-1-739-2215
  Email: Majid.iravani at wsl.ch
http://www.wsl.ch/staff/majid.iravani/

>
dfr<-data.frame(day=c("1/1/1970","5/1/1970","5/12/2003","31/12/2003"),temperature=c(1,-1,2,0.5))
> dfr
        day temperature
1   1/1/1970         1.0
2   5/1/1970        -1.0
3  5/12/2003         2.0
4 31/12/2003         0.5
>
aggregate(dfr["temperature"],by=list(format(as.Date(dfr$day,format="%d/%m/%Y"),"%m-%Y")),mean,na.rm=TRUE)
  Group.1 temperature
1 01-1970        0.00
2 12-2003        1.25
>
aggregate(dfr["temperature"],by=list(format(as.Date(dfr$Dt,format="%d/%m/%Y"),"%m")),mean,na.rm=TRUE)
  Group.1 temperature
1      01        0.00
2      12        1.25


Majid Iravani wrote:
> 
> Dear R users,
> 
> I have a dataframe with two columns: first column is date data (e.g. 
> 1/1/2000 with character format: daily data from 1/1/1970 till 31/12/2003) 
> and second column is temperature value. Now I'd like to calculate mean
for
> each month in a year (i.e. May 2001, June 1997) and mean for each month in 
> all of years. As the number of days in some months is different from
> others 
> I could not write appreciate command for this. Therefore I would greatly 
> appreciate if somebody can help me in this case
> 
> Thank you
> Majid
> 
> 
-- 
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days <- seq(as.Date("1970/1/1"), as.Date("2003/12/31"),
"days")
temp <- rnorm(length(days), mean=10, sd=8)
tapply(temp, format(days,"%Y-%m"), mean)
tapply(temp, format(days,"%b"), mean)

> -----Original Message-----
> From: r-help-bounces at stat.math.ethz.ch
> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Majid Iravani
> Sent: Thursday, February 01, 2007 8:11 AM
> To: r-help at stat.math.ethz.ch
> Subject: [R] How can I calculate conditional mean in a large
> dataset including date data
>
> Dear R users,
>
> I have a dataframe with two columns: first column is date data (e.g.
> 1/1/2000 with character format: daily data from 1/1/1970 till
> 31/12/2003)
> and second column is temperature value. Now I'd like to
> calculate mean for
> each month in a year (i.e. May 2001, June 1997) and mean for
> each month in
> all of years. As the number of days in some months is
> different from others
> I could not write appreciate command for this. Therefore I
> would greatly
> appreciate if somebody can help me in this case
>
> Thank you
> Majid
> --------------------------------------------------------------
> ------------------
>   Majid Iravani
>   PhD Student
>   Swiss Federal Research Institute WSL
>   Research Group of Vegetation Ecology
>   Z?rcherstrasse 111  CH-8903 Birmensdorf  Switzerland
>   Phone: +41-1-739-2693
>   Fax: +41-1-739-2215
>   Email: Majid.iravani at wsl.ch
> http://www.wsl.ch/staff/majid.iravani/
>
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>