[R] Summing data based on certain conditions

Fri Apr 2 16:53:07 CEST 2010

Dear Steve,

Multiplying the mean with the number of observations is essentially the same as summing the numbers.

Have a look at the plyr packages.

library(plyr)
ddply(data, c("month", "year"), function(x){
	c(MeanMultiplied = mean(x$ramm) * nrow(x), Sum = sum(x$ramm))
})

----------------------------------------------------------------------------
ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek
team Biometrie & Kwaliteitszorg
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9500 Geraardsbergen
Belgium

Research Institute for Nature and Forest
team Biometrics & Quality Assurance
Gaverstraat 4
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tel. + 32 54/436 185
Thierry.Onkelinx op inbo.be
www.inbo.be

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~ Sir Ronald Aylmer Fisher

The plural of anecdote is not data.
~ Roger Brinner

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> -----Oorspronkelijk bericht-----
> Van: r-help-bounces op r-project.org 
> [mailto:r-help-bounces op r-project.org] Namens Steve Murray
> Verzonden: vrijdag 2 april 2010 16:37
> Aan: stephan.kolassa op gmx.de; gunter.berton op gene.com
> CC: r-help op r-project.org
> Onderwerp: Re: [R] Summing data based on certain conditions
> 
> 
> Dear all,
> 
> Thanks for the contributions so far. I've had a look at these 
> and the closest I've come to solving it is the following:
> 
> > data_ave <- ave(data$rammday, by=c(data$month, data$year))
> Warning messages:
> 1: In split.default(x, g) :
>   data length is not a multiple of split variable
> 2: In split.default(seq_along(x), f, drop = drop, ...) :
>   data length is not a multiple of split variable
> 
> 
> I'm slightly confused by the warning message, as the data 
> lengths do appear the same:
> 
> > dim(data)
> [1] 1073    6
> > length(data$year)
> [1] 1073
> > length(data$month)
> [1] 1073
> 
> 
> Maybe the approach I'm taking is wrong. Any suggestions would 
> be gratefully received.
> 
> Many thanks,
> 
> Steve
> 
> 
> ----------------------------------------
> > Date: Wed, 31 Mar 2010 23:31:25 +0200
> > From: Stephan.Kolassa op gmx.de
> > To: smurray444 op hotmail.com
> > CC: r-help op r-project.org
> > Subject: Re: [R] Summing data based on certain conditions
> >
> > ?by may also be helpful.
> >
> > Stephan
> >
> >
> > Steve Murray schrieb:
> >> Dear all,
> >>
> >> I have a dataset of 1073 rows, the first 15 which look as follows:
> >>
> >>> data[1:15,]
> >> date year month day rammday thmmday
> >> 1 3/8/1988 1988 3 8 1.43 0.94
> >> 2 3/15/1988 1988 3 15 2.86 0.66
> >> 3 3/22/1988 1988 3 22 5.06 3.43
> >> 4 3/29/1988 1988 3 29 18.76 10.93
> >> 5 4/5/1988 1988 4 5 4.49 2.70
> >> 6 4/12/1988 1988 4 12 8.57 4.59
> >> 7 4/16/1988 1988 4 16 31.18 22.18
> >> 8 4/19/1988 1988 4 19 19.67 12.33
> >> 9 4/26/1988 1988 4 26 3.14 1.79
> >> 10 5/3/1988 1988 5 3 11.51 6.33
> >> 11 5/10/1988 1988 5 10 5.64 2.89
> >> 12 5/17/1988 1988 5 17 37.46 20.89
> >> 13 5/24/1988 1988 5 24 9.86 9.81
> >> 14 5/31/1988 1988 5 31 13.00 8.63
> >> 15 6/7/1988 1988 6 7 0.43 0.00
> >>
> >>
> >> I am looking for a way by which I can create monthly 
> totals of rammday (rainfall in mm/day; column 5) by doing the 
> following:
> >>
> >> For each case where the month value and the year are the 
> same (e.g. 3 and 1988, in the first four rows), find the mean 
> of the the corresponding rammday values and then times by the 
> number of days in that month (i.e. 31 in this case).
> >>
> >> Note however that the number of month values in each case 
> isn't always the same (e.g. in this subset of data, there are 
> 4 values for month 3, 5 for month 4 and 5 for month 5). Also 
> the months will of course recycle for the following years, so 
> it's not simply a case of finding a monthly total for *all* 
> the 3s in the whole dataset, just those associated with each 
> year in turn.
> >>
> >> How would I go about doing this in R?
> >>
> >> Any help will be gratefully received.
> >>
> >> Many thanks,
> >>
> >> Steve
> >>
> >>
> >>
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> >
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