[R] Problem with subset

[Luca Mortarini]

Hi,
     I am new to R and i am looking for a way to extract a subset from a
vector.
I have a vector of number oscillating around zero (a decreasing
autocorrelation function) and i would like to extract only the first
positive part of the function (from zero lag to the lag where the function
inverts its sign for the first time).
I have tried

subset(myvector,myvector>0)

but this obviously extract all the positive intervals not only the first one.
 Is there a logical statement i can use in subset? I prefer not to use an
if statement that would probably slow down the code.
Thanks a lot,
                          Luca


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dr. Luca Mortarini               l.mortarini at isac.cnr.it
Università del Piemonte Orientale
Dipartimento di Scienze e Tecnologie Avanzate