[R] Breaking up a vector

[jim holtman]

Learn how to put parentheses in expression when you do not know what
the operator precedence is:

    z <- lx[(1+(i-1)*7):((i)*7)]



On Fri, May 25, 2012 at 11:29 AM, AOLeary <aodhanol at gmail.com> wrote:
> Hi all,
>
> My problem is as follows:
>
> I want to run a loop which calculates two values and stores them in vectors
> r and rv, respectively.
> They're calculated from some vector x with length a multiple of 7.
>
> x <- c(1:2058)
>
> I need to difference the values but it would be incorrect to difference it
> all in x, it has to be broken up first. I've tried the following:
>
> r <- c(1:294)*0
> rv <- c(1:294)*0
>
> #RUN A LOOP WHERE YOU INPUT THE lx[(i-1)*7:i*7] INTO Z
> for (i in 1:294){
> #CREATE A NEW VECTOR OF LENGTH 7
> z <- NULL
> length(z)=7
> dz <- NULL
> dz2 <- NULL
>
> #STORE THE VALUES IN z
> z <- lx[1+(i-1)*7:(i)*7]
>
> #THEN DIFFERENCE THOSE
> #THIS IS r_t,i,m
> dz=diff(z)
>
> #SUM THIS UP AND STORE IT IN r, THIS IS r_t
> r[i] <- sum(dz)
>
> #SUM UP THE SQUARES AND STORE IT IN rv, THIS IS RV_t
> dz2 <- dz^2
> rv[i] <- sum(dz2)
> #END THE LOOP
> }
>
>
> However, the window seems to expand for some reason, so z ends up being a
> much longer vector than it should be and full of NAs.
>
>
> Any help or advice is much appreciated.
>
> Aodhán
>
>
> --
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>
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-- 
Jim Holtman
Data Munger Guru

What is the problem that you are trying to solve?
Tell me what you want to do, not how you want to do it.