thank you Sundar,Andy, Partha for your prompt reply.
as for the "%*%" is matrix multiplication problem sunder here is a sample of
what i want...
x <- rnorm(100,17,24) # X values
y <- rnorm(100,7,11) # Y values
# since X and Y values are independent to get their
# covariance need to multiply each of them with a Matrix say A
A <- matrix(c(10,25,8,40),nrow=2,ncol=2)
further i would like to assign both x and y vectors to one variale
say z <- c(x,y)
but if i do this my matrix multiplication fail
i.e w <- A%*%z
Error in A %*% z : non-conformable arguments ??
so it tired multiply the X and Y vector individually
x<- (A%*%x)
y<- (A%*%y)
Error in A %*% z : non-conformable arguments ??
the error persist...sunder...
or anybody who could direct me..?
regards
Kunal
Sundar Dorai-Raj <[EMAIL PROTECTED]> wrote:
>
>
> Kunal Shetty wrote:
>
> > Dear R- User
> >
> > I created two random number sets using rnorm function and calcuted their
> > respective means. However now I would like to randomly
> > replace some values with NA. Thus create my own test data.
> > Any help or suggestions on this ?
> >
> >
>
> Use ?sample:
> n <- 100
> x <- rnorm(n)
> x[sample(n, 4)] <- NA
> sum(is.na(x))
> # [1] 4
>
> > Also wanted to confirm when multiplying two random number vectors x am y by
> > matrix..is this how i do it.
> > A is the matrix
> >
> > z <- c(x,y) # x and y the two set of vectors
> >
> > w <- A%*%Z # each element in each vector multipled by the matrix .
> >
>
> (Be careful: R is case sensitive (z != Z).)
>
> I'm not really clear what you want here. "%*%" is matrix multiplication
> and "*" is elementwise multiplication. Also using "c" makes a vector or
> length "n = length(x) + length(y)". This implies that "A" above "p x n"
> (i.e. p rows, n columns) and the result "w" would be "p x 1". Please
> provide an example of what you expect to see by the multiplication.
>
> --sundar
>
> >
> > regards
> > Kunal
> >
> > ______________________________________________
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