R help - Oct 2011 - creating vector os zeros for simulations (beginner's question)

Dear R helpers,
 
I know this is a simple task, but I'm new to R and I'm still havind
difficulties with the language.
I want to create 30 vectors to be used in a simulation, each with 1 columm and 5
lines, of random numbers N(0,1).
What I tried was this:
 
N=150
u2<-rep(1:150,0)
u2<-list(matrix(0,5))
u2
for(i in 1:N)
{
u2[i]<-rnorm(5)
}
u2

### also tried this:

N=150
u2<-rep((matrix(0,5)),30)
u2
for(i in 1:N)
{
u2[i]<-rnorm(5)
}
u2

 
The problem is none of this gives me the random numbers arranged in vectors.
I've tried other variations too, but haven't managed to get it through.
 
Any help is very welcome.
Kind regards,
Iara
	[[alternative HTML version deleted]]

you could try this:

u2=matrix(rnorm(150), nrow=5, ncol=30); u2

Seb



On Thu, Oct 27, 2011 at 1:44 PM, Iara Faria <iaragohn at yahoo.com.br>
wrote:
> Dear R helpers,
>
> I know this is a simple task, but I'm new to R and I'm still havind
difficulties with the language.
> I want to create 30 vectors to be used in a simulation, each?with 1 columm
and 5 lines, of random numbers N(0,1).
> What I tried was this:
>
> N=150
> u2<-rep(1:150,0)
> u2<-list(matrix(0,5))
> u2
> for(i in 1:N)
> {
> u2[i]<-rnorm(5)
> }
> u2
>
> ### also tried this:
>
> N=150
> u2<-rep((matrix(0,5)),30)
> u2
> for(i in 1:N)
> {
> u2[i]<-rnorm(5)
> }
> u2
>
>
> The problem is none of this gives me the random numbers arranged in
vectors.
> I've tried other variations too, but haven't managed to get it
through.
>
> Any help is very welcome.
> Kind regards,
> Iara
> ? ? ? ?[[alternative HTML version deleted]]
>
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
>

Thank you all very much, specially Ellison.
 
I have been looking at some codes for simulation and I am trying to recreate
them to my needs, but I understand I'm probably not doing it in the most
efficient way.
What you said was very useful.
I really want to create a series of vector of random numbers, because later I
will multiply them to a matrix P (choleski decomposition of variance-covariance
of the residuals of a VAR), so to create a serie of vectors of shocks that will
be added to my predictions.
The thing is, I wasn't able to construct the vectors of random numbers in a
way they could be multiplied by the matrix P .
 
Would you be so kind as to point again what is wrong?
I am finding it very difficult to get it right in terms of what the object must
be to be used the way I want, a list, a data.frame, matrix, etc
 
What I want to do is this:
1 - create a serie of N random vectors (actually, each 5 colums and 1 row), in
this exercise N=30
2 - Create the serie P, by multiplying each of the random vectors by the same
matrix c (choleski decomposition), which is 5x5, to get the shocks that consider
the correlation between the variables.
3 - Create serie prev, with the predictions one step ahead of the variables, by
multiplying the matrix coef (coefficients of the VAR) to the last prediction and
adding the vector P of shocks.
 
What I tried was:
# 1- different ways of creating the random vectors, to see if any multiply by c:
N=30 # N = numero de periodos para computar a trajetoria da divida
u2<-list()
for(i in 1:N) u2[[i]] <- rnorm(5)
u2
str(u2)
 
u3 <- as.data.frame(matrix(rnorm(150), nrow=N, ncol=5))
u3
str(u3)
 
u4<-list()
for (i in 1:N) {
 u4[[i]]<- matrix(rnorm(150), ncol=5, nrow=N)
}
u4

# 2- create serie P, of shocks ajusted by the correlations
P2<-matrix(0, ncol=N, nrow=5)
P2
for(i in 1:N){
 P2[i]<-c%*%u2[i]
}
#but this is what i get:
Error in c %*% u2[i] : requires numeric/complex matrix/vector arguments
# i've tried taking out the [i], that doesn't work either.
# tried also u3, u4....
# obs- c is matrix 5x5:
> c
                 rp        igpm        ereal      crescpib     jurosreal
rp        0.2249159 -0.02046234  0.004685928 -0.0002799183  2.639328e-04
igpm      0.0000000  0.59823056 -0.577864072  0.0070967189 -5.797647e-03
ereal     0.0000000  0.00000000  0.129118968  0.0007949951 -1.061969e-04
crescpib  0.0000000  0.00000000  0.000000000  0.0236250353  2.646392e-05
jurosreal 0.0000000  0.00000000  0.000000000  0.0000000000  2.027526e-03
 
# 3 - create serie previ2, size=N, 
# obs - prev2[1] = vector z, of last observations
prev2<-c(z,rep(0,100))
prev2
for (i in 2:N) {
 prev2[i]<-coef%*%prev2[i-1]+P2[i]
}
 
 
Once again, thank you very much for the kind help.
 
Regards,
Iara

________________________________
De: S Ellison <S.Ellison@LGCGroup.com>

Enviadas: Sexta-feira, 28 de Outubro de 2011 8:02
Assunto: RE: [R] creating vector os zeros for simulations (beginner's
question)


> -----Original Message-----
> On Thu, Oct 27, 2011 at 1:44 PM, Iara Faria 
> > Dear R helpers,
> >
> > I know this is a simple task, but I'm new to R and I'm 
> still havind difficulties with the language.
> > I want to create 30 vectors to be used in a simulation, 
> each with 1 columm and 5 lines, of random numbers N(0,1).
> > What I tried was this:
> >
> > N=150
> > u2<-rep(1:150,0)
> > u2<-list(matrix(0,5))
> > u2
> > for(i in 1:N)
> > {
> > u2[i]<-rnorm(5)
> > }
> > u2
This line
> > u2[i]<-rnorm(5)
should be written
u2[[i]]<-rnorm(5)

u2[i] is a list element and ur[[i]] is the contents of the list element. Not
quite the same thing.

Your code could also be a great deal simpler as you don't need to generate a
zero-filled list to start with. Try

u2<-list()
for(i in 1:N) u2[[i]] <- rnorm(5)

But it's easier to generate the matrix version as Seb said.

If you _really_ want a list - which can be useful, but is often unnecessary if
you use apply() - you can also do
u2 <- as.data.frame(matrix(rnorm(150), nrow=5, ncol=30))

which, since a data frame is a list, is also a list.

And while we're on the topic, look at lapply and other versions of apply
be[[elided Yahoo spam]]


> > ### also tried this:
> >
> > N=150
> > u2<-rep((matrix(0,5)),30)
> > u2
> > for(i in 1:N)
> > {
> > u2[i]<-rnorm(5)
> > }
> > u2
> >
> >
> > The problem is none of this gives me the random numbers 
> arranged in vectors.
> > I've tried other variations too, but haven't managed to get 
> it through.
> >
> > Any help is very welcome.
> > Kind regards,
> > Iara
> >        [[alternative HTML version deleted]]
> >
> >
> > ______________________________________________
> > R-help@r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide 
> > http://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained, reproducible code.
> >
> >
> 
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide 
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
> *******************************************************************
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