Hello,
Inline
Em 17-08-2012 04:39, bantex escreveu:
Hi guys,
After a long while I came up with this :
set.seed(2)
a<-matrix(rnorm(4),ncol=2)
abc<-function(a)
{
b=matrix(NA,nrow=3,ncol=3)
b[1,1]=a[1,1]+1
b[1,2]=a[2,1]*a[2,2]
b[1,3]=a[2,2]+a[1,1]
b[2,1]=a[1,1]-5
b[2,2]=sqrt(a[2,2])
b[2,3]=a[1,1]/a[2,2]
b[3,1]=a[2,2]-3
b[3,2]=a[1,1]*(a[1,2]+a[2,2])
b[3,3]=sqrt(a[1,1])/a[1,2]
return(b=matrix(c(b[1,1],b[1,2],b[1,3],b[2,1],b[2,2],b[2,3],
b[3,1],b[3,2],b[3,3]),ncol=3))
You don't need to say that 'b' is a matrix a second time! And this form
is wrong, you should add 'byrow = TRUE' since you're using row order.
}
How can I improve on it?
With your data, you would have two errors in applying function abc to
matrix 'a'. Try the following.
fun <- function(a){
b <- matrix(nrow = 3, ncol = 3)
#let's say these are the transformations i wish to perform
b[1,1] <- a[1,1]+1
b[1,2] <- a[2,1]*a[2,2]
b[1,3] <- a[2,2]+a[1,1]
b[2,1] <- a[1,1]-5
if(a[2,2] < 0){
warning("a[2, 2] is negative, using zero for its square root
b[2,2].")
b[2,2] <- 0
}else{
b[2,2] <- sqrt(a[2,2])
}
if(a[2,2] == 0){
warning("a[2, 2] is zero, using zero for division result b[2,3].")
b[2,3] <- 0
}else{
b[2,3] <- a[1,1]/a[2,2]
}
b[3,1] <- a[2,2]-3
b[3,2] <- a[1,1]*(a[1,2]+a[2,2])
if(a[1,2] == 0){
warning("a[1, 2] is zero, using zero for division result b[3,3].")
b[3,3] <- 0
}else if(a[1,1]/a[1,2] < 0){
warning("a[1,1]/a[1,2] is negative, using zero for its square
root b[3,3].")
b[3,3] <- 0
}else{
b[3,3] <- sqrt(a[1,1]/a[1,2])
}
b
}
set.seed(2)
a <- matrix(rnorm(4),ncol = 2)
fun(a)