[R] apply family functions (tapply, sapply, mapply etc)

[Dimitris.Kapetanakis]

Dear all,

I am trying to use apply or similar functions in order to improve the
efficiency of my code but I guess I am misunderstanding the function of
these commands. What I want to do is possible to see with the following code
that I use a for loop command. In words what I want to do are two things 1)
to multiply each row of a matrix with its transpose (the same row in a
column) for each row the matrix. 

N<-250
x.1<-as.matrix(rnorm(N,0,1))												
x.2<-as.matrix(rnorm(N,1,1))												
x.3<-as.matrix(rnorm(N,1,1))												
x.4<-as.matrix(rnorm(N,0,1))												
X<-cbind(x.1, x.2,x.3,x.4)
q<-ncol(X)-1	
h0<-0.3														
Xu<-cbind(x.1,x.2,x.3)																		
beta.in<-as.matrix(c(1,1,1))

XX<-matrix(0,N*q,q)
Qn<-matrix(0,N*q,q)
DDS<-function(Betas, h, Xs){
	v<-(Xs[,1:q]%*%Betas+Xs[,q+1])/h
	((105/64)*(matrix(1,N,1)-10*v+28*v^3-18*v^5)*(v>-1)*(v<1))}

for (j in 1:N){
	nq<-(j-1)*q+1
	nq1<-j*q
	Qn[nq:nq1,]<-Xu[j,]%*%t(Xu[j,])*(DDS(beta.in, h=h0, Xs=X)[j,])
	XX<-Xu[j,]%*%t(Xu[j,])
}

for (j in 1:N){
		nq<-(j-1)*q+1
		nq1<-j*q
		Q<-0+Qn[nq:nq1,]
}


Another issue that I try to solve is that I want to calculate the result of
let say a function "S" for every different row of the matrix, lets call it
B, where the rows of B I want to be the argument Betas (that is a vector) of
function "S"


Sn  <-function(Betas, h, Xs){
	v<-(Xs[,1:q]%*%Betas+Xs[,q+1])/h

(2*Y-1)*(0.5+(105/64)*(v-(5/3)*v^3+(7/5)*v^5-(3/7)*v^7))*(v>-1)*(v<1)+matrix(1,N,1)*(v>=1)}
	
S  <-function(Betas, h, Xs){colMeans(Sn(Betas, h, Xs))}

Any help would be highly appreciated

Thanks

Dimitris


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