[R] creating a certain type of matrix

[Petr Pikal]

Hi

as only you know perfectly which halves and other portions of your 
matrices contain zeroes and which contain random numbers you has to 
finalize the function yourself.
Here are few ideas.

n<-20
mat<-matrix(0,n,(n/2)/5+1) #matrix of zeroes
dd<-dim(mat) # actual dimensions
mat[1:(dd[1]/2),1]<-1 #put 1 in first half of first column
mat[((dd[1]/2)+1):dd[1],1]<-rnorm(dd[1]/2,0,1) #put random numbers in 
following part of the matrix column 1
mat[((dd[1]/2)+1):(dd[1]/2)+dd[1]/4,2]<-rnorm(dd[1]/4,0,1) #put 
random numbers in column2

than according to n and dd values you can put any numbers anywhere in 
your matrix e.g. in for loop (not.tested :-)

for (i in 3:dd[2]) {

arrange everything into following desired columns
e.g.

length.of.rand.numbers <- (i-2)*5
my.rand.num<- rnorm(length.of.rand.numbers, 0,1)
start <- dd[1]/2+dd[1]/4
end <- start + length.of.rand.numbers
mat[start:end, i]<- my.rand.num

}

HTH
Petr

On 7 Feb 2006 at 0:07, Taka Matzmoto wrote:

From:           	"Taka Matzmoto" <sell_mirage_ne at hotmail.com>
To:             	r-help at stat.math.ethz.ch
Date sent:      	Tue, 07 Feb 2006 00:07:11 -0600
Subject:        	[R] creating a certain type of matrix

> Hi R users
> 
> I like to generate a certain type of  matrix.
> If there are 10 variables, the matrix will have nrow=10,
> ncol=((10/2))/5+1. so the resulting matrix's dimension 10 by 2. If
> there are 50 variables the dimension of the resulting matrix will be
> 50 by 6.
> 
> The arrangement of elements of this matrix is important to me and I
> can't figure out how to arrange elements.
> 
> If I have 20 variables. The resulting matrix will be 20 by 3
> The first half of first column of the matrix will be 1s. The all
> elements on the second half of the first column of the matrix will be
> random numbers coming from rnorm(1,0,1). The first half of the second
> column of the matrix will be zeros. The first five elements of the
> second half of the second column of the matrix will be random numbers
> coming from rnorm(1,0,1). After that, the remaining elements of the
> second half will be zeros. The first half of the third column of the
> matrix will be zeors. The first five elements of the second half of
> the third column will be zeros too and then 5 random numbers coming
> from rnorm(1,0,1).
> 
> If there are 40 variables the resulting matrix will be 40*5
> The first half of first column of the matrix will be 1s. The all
> elements on the second half of the first column of the matrix will be
> random numbers coming from rnorm(1,0,1).
> 
> The first half of the second column of the matrix will be zeros. The
> first five elements of the second half of the second column of the
> matrix will be random numbers coming from rnorm(1,0,1). After that,
> the remaining elements of the second half will be zeros.
> 
> The first half of the third column of the matrix will be zeors. The
> first FIVE elements of the second half of the third column will be
> zeros too and then 5 random numbers coming from rnorm(1,0,1) and then
> the rest of elements of the third column will be zeros.
> 
> The first half of the fourth column of the matrix will be zeors.The
> first TEN elements of the second half of the fourth column will be
> zeros too and then 5 random numbers coming from rnorm(1,0,1) and then
> the rest of elements of the third column will be zeros.
> 
> The first half of the fifth column of the matrix will be zeors.The
> first FIFTEEN elements of the second half of the fourth column will be
> zeros too and then 5 random numbers coming from rnorm(1,0,1).
> 
> I tried to create 10 different functions ( one for 10, 20, 30, 40,
> .... , 100 variables) but it's not efficient.
> 
> Any help or advice for creating one function that can do all 10 kind
> of variable cases would be appreciated.
> 
> Thans in advance
> 
> Taka
> 
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Petr Pikal
petr.pikal at precheza.cz