R help - Aug 2009 - Counting the number of non-NA values per day

I have a long dataframe ("pollution") that contains a column of hourly
date information ("date") and  a column of  pollution  measurements
("pol")

I have been happily calculating daily means and daily maximums using the 
aggregate function

 DMEANpollution =  aggregate(pollution["pol"], 
format(pollution["date"],"%Y-%j"), mean, na.rm = TRUE)
 DMAXpollution =  aggregate(pollution["pol"], 
format(pollution["date"],"%Y-%j"), max, na.rm = TRUE)

However, I also need to count the number of valid measurements for each 
day to check that the mean and max are likely to be valid (for example I 
need at least 18 hourly measurements to calculate a valid daily mean)

Try as I might I have not found a simple way of doing this.
Can anybody help please?

Many thanks,
Tim.

-- 


__________________________________________

Dr Tim Chatterton
Senior Research Fellow
Air Quality Management Resource Centre
Faculty of Environment and Technology
University of the West of England
Frenchay Campus
Bristol
BS16 1QY

Tel: 0117 328 2929
Fax: 0117 328 3360
Email: Tim.Chatterton at uwe.ac.uk

Try 

tempFun <- function(x) sum(!is.na(x))
nonZeros <- 
aggregate(pollution["pol"],format(pollution["date"],"%Y-%j"),
FUN = tempFun)

--- On Wed, 12/8/09, Tim Chatterton <tim.chatterton at uwe.ac.uk> wrote:
> From: Tim Chatterton <tim.chatterton at uwe.ac.uk>
> Subject: [R] Counting the number of non-NA values per day
> To: r-help at r-project.org
> Received: Wednesday, 12 August, 2009, 3:26 AM
> I have a long dataframe ("pollution")
> that contains a column of hourly date information ("date")
> and? a column of? pollution? measurements
> ("pol")
> 
> I have been happily calculating daily means and daily
> maximums using the aggregate function
> 
> DMEANpollution =? aggregate(pollution["pol"],
> format(pollution["date"],"%Y-%j"), mean, na.rm = TRUE)
> DMAXpollution =? aggregate(pollution["pol"],
> format(pollution["date"],"%Y-%j"), max, na.rm = TRUE)
> 
> However, I also need to count the number of valid
> measurements for each day to check that the mean and max are
> likely to be valid (for example I need at least 18 hourly
> measurements to calculate a valid daily mean)
> 
> Try as I might I have not found a simple way of doing
> this.
> Can anybody help please?
> 
> Many thanks,
> Tim.
> 
> -- 
> 
> __________________________________________
> 
> Dr Tim Chatterton
> Senior Research Fellow
> Air Quality Management Resource Centre
> Faculty of Environment and Technology
> University of the West of England
> Frenchay Campus
> Bristol
> BS16 1QY
> 
> Tel: 0117 328 2929
> Fax: 0117 328 3360
> Email: Tim.Chatterton at uwe.ac.uk
> 
> ______________________________________________
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