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

[Ptit_Bleu]

Hello Ravi,

I was also trying to write down such a calculation but I did not manage (I
didn't use diff(x)).
Thank you for the solution.
Ptit Bleu.



Ravi Varadhan wrote:
> 
> Here is a simple trapezoidal rule integrator:
> 
> x <- time
> y <- value
> 
> area <- sum(diff(x)*(y[-1]+y[-length(y)]))/2
> 
> Ravi.
> 
> 
> ----------------------------------------------------------------------------
> -------
> 
> 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
> 
> 
> 
> ----------------------------------------------------------------------------
> --------
> 
> -----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.
>> -- 
>> View this message in context:
>>
> http://www.nabble.com/Must-be-easy%2C-but-haven%27t-found-the-function-%28nu
> merical-integration%29-tf4465684.html#a12732936
>> Sent from the R help mailing list archive at Nabble.com.
>> 
>> ______________________________________________
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>> 
>> 
> 
> -- 
> View this message in context:
> http://www.nabble.com/Must-be-easy%2C-but-haven%27t-found-the-function-%28nu
> merical-integration%29-tf4465684.html#a12759423
> Sent from the R help mailing list archive at Nabble.com.
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
> 
> 

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