# Re: [R] (second round) creating a certain type of matrix

Date: Wed 08 Feb 2006 - 23:05:36 EST

generate.matrix <- function(nr, runs=5){

```   h   <- nr/2                                ## half of nr
```
nc <- nr/10 + 1
```   mat <- matrix(0, nr, nc)                   ## initialize

mat[ ,1] <- c( rep(1, h), rnorm(h) )       ## 1st column
mat[ (h+1):(h+5), 2] <- rnorm(5)           ## 2nd column

if( nc > 3 ){
for (i in 3:nc){                          ## column 3 - end

start <-  h + 5*(i-2) + 1
end   <-  start + runs - 1

mat[ start:end, i] <- rnorm( runs )
```
}
}
return(mat)
}

However you can simplify this greatly. If you ignore the first column (which looks like some initialisation column in simulation process), then you have a matrix with nr/2 rows and nr/10 columns with diagonal blocks 5 runs filled with rnorm values. Here is what I propose :

gen.mat <- function(x, runs=5){

if( (x %% 2*runs)!=0 ) stop(x, " is not a multiple of ", 2*runs)

nr <- x/2
nc <- x/(2*runs)

mat <- matrix(0, nr, nc)
for (i in 1:nc) mat[ ((i-1)*runs + 1) : (i*runs), i ] <- rnorm(runs)

```   down <- cbind( rnorm(nr), mat )
top  <- cbind( 1, matrix( 0, nr=nr, nc=nc ) )
out  <- rbind( top, down )

```

return(out)
}

# Examples

``` gen.mat(50)
gen.mat(55)         ## should generate an error
gen.mat(24, runs=6)

```

Does this function do what you want to ?

On Tue, 2006-02-07 at 11:03 -0600, Taka Matzmoto wrote:
> Hi R users
> Here is what I got with help from Petr Pikal (Thanks Petr Pikal). I modified
> Petr Pikal's code to a little
> to meet my purpose.
>
> I created a function to generate a matrix
>
> generate.matrix<-function(n.variable)
> {
> mat<-matrix(0,n.variable,(n.variable/2)/5+1) #matrix of zeroes
> dd<-dim(mat) # actual dimensions
> mat[1:(dd/2),1]<-1 #put 1 in first half of first column
> mat[((dd/2)+1):dd,1]<-rnorm(dd/2,0,1) #put random numbers in
> following part of the matrix column 1
> mat[((dd/2)+1):((dd/2)+5),2]<-rnorm(5,0,1) #put random numbers in
> column2
> for (i in 3:(dd))
> {
> length.of.rand.numbers <- 5
> my.rand.num<- rnorm(length.of.rand.numbers, 0,1)
> start <- dd/2+5*(i-2)+1
> end <- start + length.of.rand.numbers-1
> mat[((start):end), i]<- my.rand.num
> }
> mat
> }
>
> Do you (any R users) have any suggestion to this function to make this
> function work better or efficiently?
>
> Taka
> It works but I
>
> >From: "Petr Pikal" <petr.pikal@precheza.cz>
> >To: "Taka Matzmoto" <sell_mirage_ne@hotmail.com>,r-help@stat.math.ethz.ch
> >Subject: Re: [R] creating a certain type of matrix
> >Date: Tue, 07 Feb 2006 08:58:59 +0100
> >MIME-Version: 1.0
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> >
> >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/2),1]<-1 #put 1 in first half of first column
> >mat[((dd/2)+1):dd,1]<-rnorm(dd/2,0,1) #put random numbers in
> >following part of the matrix column 1
> >mat[((dd/2)+1):(dd/2)+dd/4,2]<-rnorm(dd/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) {
> >
> >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/2+dd/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@hotmail.com>
> >To: r-help@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
> > >
> > > ______________________________________________
> > > R-help@stat.math.ethz.ch mailing list
> > > https://stat.ethz.ch/mailman/listinfo/r-help
> > > http://www.R-project.org/posting-guide.html
> >
> >Petr Pikal
> >petr.pikal@precheza.cz
> >
>
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