Calculate Eigenvalues of a given matrix m.
> sm <- eigen(m, sym=TRUE) > V <- sm$vectors > t(V) %*% V > V %*% diag(sm$values) %*% t(V)
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Delete particular rows from matrix.
> x <- matrix(1:10,,2) > x[x[,1]%in%c(2,3),] > x[!x[,1]%in%c(2,3),]
from Peter Malewski or from Peter Dalgaard:
> mat[!(mat$first %in% 713:715),]
Create a multidimensional matrix.
Brian Ripley said:
will give you a 4-dimensional 10 x 5 x 6 x 8 array.
Or
> my.array<-array(0,dim=c(10,5,6,8))
will give you a 4-dimensional 10 x 5 x 6 x 8 array.
Or
> array.test <- array(1:64,c(4,4,4)) > array.test[1,1,1] > 1 > array.test[4,4,4] > 64
Create an identity matrix.
> diag(n)
Or the long way:
> n<-c(5) > I <- matrix(0,nrow=n,ncol=n) > I[row(I)==col(I)] <- 1
Create a vector, append values.
To create a mathematical vector, you can just initialize a column of numbers with c(). As long as all of your input is of the same type, you don't hit any snags. Note the is.vector() function will say this is a vector:
> v <- c(1, 2, 3) > is.vector(v)
Remove a trailing pathname component, leaving the head
$ echo =ls(:h) /bin
Hello World - C
#include <stdio.h> main() { for(;;) { printf ("Hello World!\n"); } }
