Kunal Shetty wrote:
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..?
Of course this doesn't work. `A' is 2x2, `x' and `y' are 100x1, and `z' is 200x1 (I think I even mentioned this previously). I *think* you want something like:
z <- rbind(x, y) # now 2 x 100
w <- A %*% z # 2 x 100
If not, please provide an example of what you expect, possibly worked by hand.
HTH,
--sundar
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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