[R] Calculation of daily max

Augusto.Sanabria@ga.gov.au Augusto.Sanabria at ga.gov.au
Wed Jan 18 03:57:24 CET 2006

Thank you Gabor, the 'aggregate' function
operating on zoo(WS) does the job beautifully!

'zoo' has a lot of other goodies too, great 
package (thanks for that too).



Augusto Sanabria. MSc, PhD.
Mathematical Modeller
Risk Research Group
Geospatial & Earth Monitoring Division
Geoscience Australia (www.ga.gov.au)
Cnr. Jerrabomberra Av. & Hindmarsh Dr.
Symonston ACT 2609
Ph. (02) 6249-9155

-----Original Message-----
From: Gabor Grothendieck [mailto:ggrothendieck at gmail.com] 
Sent: Tuesday, 17 January 2006 4:32 PM
To: Sanabria Augusto
Cc: r-help at stat.math.ethz.ch
Subject: Re: [R] Calculation of daily max

Assuming VDATE is a character vector this produces
a zoo time series object.

	z <- aggregate(zoo(WS), as.Date(VDATE), max)

coredata(z) and time(z) are the data vector of maximums and corresponding
times, respectively.

The R command:


gives an introduction to zoo.

Aside from zoo you could check out ?tapply, ?by and ?aggregate .

On 1/16/06, Augusto.Sanabria at ga.gov.au <Augusto.Sanabria at ga.gov.au> wrote:
> Good day everyone.
> I have a large dataset of 1 min wind speeds
> covering 5 years.
> How can I make an array of maximum daily values?
> The vectors I have are: 'VDATE' with dates in format '%Y-%m-%d' (like 
> '1992-10-28') and 'WS' with wind speed data (same number of elements 
> as VDATE).
> I want an array with 2 columns: Max daily wind speed and corresponding 
> day.
> Has anyone got an elegant way of doing that?
> (My background is in C++ I would tend to use loops
> but that is not very elegant in R, isn't it?)
> Augusto
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