[R] programming to calculate variance

[Eik Vettorazzi]

Hi Marlene,

x=data.frame(y,vr=NA)
for(i in 4:nrow(x)) x[i,"vr"] =var(y[(i-3):(i-1)])

will do the trick, solving both problems with overwriting subsequent 
x-values and obeying the precedence of R operators.
For the latter, see ?Syntax and compare
i<-5
i-3:i-1
(i-3):(i-1)

hth.

marlene marchena schrieb:
> Dear R-user
>
> Suppose I have the following data
>
>  y=c(2,1,5,8,11,3,1,7,50,21,33,7,60)
>
> x=data.frame(y)
>
> for(i in 4:nrow(x)) x[i,] =var(x[i-3:i-1,])
>
> I'm trying to get a new variable with the variance of the 3 previous values
> (just an example) and with NA in the three first positions. I know that my
> for() is wrong
> but I'm not able to find my error.
>
> Any idea?
>
> Thanks,
>
> Marlene.
>
> 	[[alternative HTML version deleted]]
>
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> and provide commented, minimal, self-contained, reproducible code.
>   

-- 
Eik Vettorazzi
Institut für Medizinische Biometrie und Epidemiologie
Universitätsklinikum Hamburg-Eppendorf

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