R: LIST function and LOOPS

hi 

thanx for the help. i dont want to use matrices. i solve my problem, see
the example below.

the set.seed is used because in my actual application i need to generate
INDEPENDENT variables. will this ensure that the variables are
independent? 

z3<-function(w)
{
for (i in 1:w)
{
ss<-0
       for (j in 1:5)
       {
                set.seed(j+1+(i-1)*6)
                r<-rnorm(1)
        	ss<-ss+r
		a<-list(ss=ss,r=r)
       }
print(paste("############ i=",i,"############"))
print(a)
}
}
z3(3)

z3(3)

[1] "############ i= 1  ############"
$ss
[1] -2.213343

$r
[1] 0.269606

[1] "############ i= 2  ############"
$ss
[1] -2.904235

$r
[1] -1.480568

[1] "############ i= 3  ############"
$ss
[1] -0.01516304

$r
[1] 0.9264592


thanx again

***
allan

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Adaikalavan Ramasamy wrote:

You will need to capture the value of ss at the end of each 'i' as such

z4 <-function(w){

 output <- numeric(w)

 for (i in 1:w){

   set.seed(i+6)  # this is redundant line
   ss<-0

   for (j in 1:5){
     set.seed(j+1+(i-1)*6)
     r<-rnorm(1)
     ss<-ss+r
   }

   output[i] <- ss
 }
 return(output)
}

BTW, I do not think it is a good idea to set.seed() so many times.

To answer you more general question, see if the following is useful.
I am trying to simulate 'n' values from a standard normal distribution
but 'n' is random variable itself.

f <-function(w, lambda=3){

 tmp <- list(NULL)

 for (i in 1:w){
   n <- 1 + rpois(1, lambda=lambda)  # number of simulation required
   tmp[[ i ]]  <- rnorm(n)
 }

 # flatten the list into a ragged matrix
 out.lengths   <- sapply(tmp, length)
 out           <- matrix( nr=w, nc=max( out.lengths ) )
 rownames(out) <- paste("w =", 1:w)
 for(i in 1:w) out[i, 1:out.lengths[i] ] <- tmp[[i]]

 return(out)
}

f(6, lambda=3)

It is not very elegant but I hope that helps you out somehow.

Regards, Adai

On Thu, 2005-03-10 at 10:16 +0200, Clark Allan wrote:

hi all

another simple question.

i've written a dummy program so that you get the concept. (the code
could be simplfied such that there are no loops. but lets leave the
loops in for now.)

z1<-function(w)
{
for (i in 1:w)
{
set.seed(i+6)
ss<-0
     for (j in 1:5)
     {
             set.seed(j+1+(i-1)*6)
             r<-rnorm(1)
             ss<-ss+r
     }
list(ss=ss)
}
}
check.1<-z1(3)
check.1

the results is:
$ss
[1] -0.01516304


what i want is something that looks like this:

j=1
$ss
[1] -2.213343

j=2
$ss
[1] -2.904235

j=3
$ss
[1] -0.01516304


i know that i could use the print command. (see z2)

z2<-function(w)
{
for (i in 1:w)
{
set.seed(i+6)
ss<-0
     for (j in 1:5)
     {
             set.seed(j+1+(i-1)*6)
             r<-rnorm(1)
             ss<-ss+r
     }
print(ss)
}
}
check.2<-z2(3)
check.2

check.2<-z2(3)

[1] -2.213343
[1] -2.904235
[1] -0.01516304

check.2

[1] -0.01516304

the problem with z2 is that only the last value is saved.


what i could do is use matrices like the following: (but i dont want to
do this AND WOULD PREFER TO USE list.)

z3<-function(w)
{
results.<-matrix(nrow=w,ncol=1)
colnames(results.)<-c("ss")
for (i in 1:w)
{
set.seed(i+6)
ss<-0
     for (j in 1:5)
     {
             set.seed(j+1+(i-1)*6)
             r<-rnorm(1)
             ss<-ss+r
     }
results.[i,1]<-ss
}
results.
}
check.3<-z3(3)
check.3

check.3

             ss
[1,] -2.21334260
[2,] -2.90423463
[3,] -0.01516304

what if i have a new program (something different) and i want the
following:

j=1
$a
1
2
3

$b
1
2
3
4
5

$c
1


###############
j=2
$a
11
21
31

$b
11
21
31
41
51

$c
11

###############
j=3
$a
21
22
32

$b
21
22
32
42
52

$c
21

MATRICES SEEMS TO BE A GOOD WAY OF DOING THIS (but then you would have
to set up three matrices, one for a,b and c). BUT WHAT IF I WANT TO USE
THE LIST FUNCTION? i.e. there is a list in the first loop that i want to
display!

sorry for the long mail.

***
ALLAN