simple loop iteration

Hi R mailing list,

probably a very basic problem here, I try to do the following:

Q<-c(1,2,3)
P<-c(4,5,6)
A<- data.frame(Q,P)
A

?Q P
1 1 4
2 2 5
3 3 6

this is my simplified data.frame (matrix) now I try to create following
loop for subtraction of element within the data.frame:

for(i in length(A[,"P"]-1){

?delta[i]<- A[i,"P"]-A[i+1,"P"]
}

All I get is a vector of ?the correct length but with no readings.

Thanks for any help on this.



--
Niklaus H?rlimann

Universit? de Lausanne
Institut de Min?ralogie et G?ochimie
L'Anthropole
CH-1015 Lausanne
Suisse

E-mail: Niklaus.Hurlimann at unil.ch
Tel:+41(0)21 692 4452

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