[R] RE : Must be easy, but haven't found the function (numerical integration)

[Ravi Varadhan]

Here is a simple trapezoidal rule integrator:

x <- time
y <- value

area <- sum(diff(x)*(y[-1]+y[-length(y)]))/2

Ravi.


----------------------------------------------------------------------------
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Ravi Varadhan, Ph.D.

Assistant Professor, The Center on Aging and Health

Division of Geriatric Medicine and Gerontology 

Johns Hopkins University

Ph: (410) 502-2619

Fax: (410) 614-9625

Email: rvaradhan at jhmi.edu

Webpage:  http://www.jhsph.edu/agingandhealth/People/Faculty/Varadhan.html



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-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On
Behalf Of Ptit_Bleu
Sent: Tuesday, September 18, 2007 11:24 AM
To: r-help at r-project.org
Subject: Re: [R] RE : Must be easy, but haven't found the function
(numerical integration)


Thanks to all.

cumsum can be helpful but the solution given by David seems to match my
request.
I will test it as soon as possible (before the end of the week, I hope).

Have a nice end of day,
Ptit Bleu.



GOUACHE David wrote:
> 
> try :
> 
> library(Bolsatd)
> ?sintegral
> 
> or:
> 
> library(caTools)
> ?trapz
> 
> David Gouache
> Arvalis - Institut du Végétal
> Station de La Minière
> 78280 Guyancourt
> Tel: 01.30.12.96.22 / Port: 06.86.08.94.32
> 
> 
> -----Message d'origine-----
> De : Ptit_Bleu [mailto:ptit_bleu at yahoo.fr] 
> Envoyé : lundi 17 septembre 2007 12:09
> À : r-help at stat.math.ethz.ch
> Objet : [R] Must be easy,but haven't found the function (numerical
> integration)
> 
> 
> Hi,
> 
> I have a data frame of 2 columns with the following types :
> data$day char
> data$value num
> 
> And I plot my data with :
> plot(strptime(donnees$day,format="%Y-%m-%d %H:%M:%S"),donnees$value,
> type="l")
> 
> And I'd just like to get the numerical value of the integration of this
> graph.
> I looked at ?integrate but, as far as I understood (that is, not very
> much,
> due to my poor english), it seems that it doesn't work with values in data
> frame.
> 
> Could you please help me to do this ?
> 
> Thanks in advance,
> Have a nice week,
> Ptit Bleu.
> -- 
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merical-integration%29-tf4465684.html#a12732936
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