R help - Feb 2007 - matrix manipulations

Dear friends,

I have a basic question with R. I'm generating a set
of random variables and then combining them using the
cbind statement. The code for that is given below.

for (i in 1:100)
  {
    y <- rpois(i,lambda=10)
    X0 <- seq(1,1,length=i)
    X1 <- rnorm(i,mean=5,sd=10)
    X2 <- rnorm(i,mean=17,sd=12)
    X3 <- rnorm(i,mean=3, sd=24)
    ind <- rep(1:5,20)
  }
  
data100 <- cbind(y,X0,X1,X2,X3,ind)

but when i look at the data100 table, the y values now
take the observation count. (ie) the data under Y is
not the poisson random generates but the observation
number. Hence the last vector (ind) does not have a
header. Is there any way i can drop the number of
observation counts being added into the matrix.

Thanks in advance for your help.

Sincerely

Anup



"However bad life may seem, there is always something you can do and
succeed at. While there is life, there is hope." Stephen Hawking

Anup Menon Nandialath
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Anup Nandialath wrote:
> Dear friends,
>
> I have a basic question with R. I'm generating a set
> of random variables and then combining them using the
> cbind statement. The code for that is given below.
>
> for (i in 1:100)
>   {
>     y <- rpois(i,lambda=10)
>     X0 <- seq(1,1,length=i)
>     X1 <- rnorm(i,mean=5,sd=10)
>     X2 <- rnorm(i,mean=17,sd=12)
>     X3 <- rnorm(i,mean=3, sd=24)
>     ind <- rep(1:5,20)
>   }
>   
> data100 <- cbind(y,X0,X1,X2,X3,ind)
>
> but when i look at the data100 table, the y values now
> take the observation count. (ie) the data under Y is
> not the poisson random generates but the observation
> number. Hence the last vector (ind) does not have a
> header. Is there any way i can drop the number of
> observation counts being added into the matrix.
>
>   
That is not what is going on. Sounds like you have your column labels 
misaligned with the column contents.

Take a look at

m <- matrix(rnorm(4), 2, 2)
m
colnames(m) <- c("a", "b")
m
dim(m)

(what was that for loop supposed to be good for, by the way?)

Anup Menon Nandialath wrote:
> 
> I have a basic question with R. I'm generating a set
> of random variables and then combining them using the
> cbind statement. The code for that is given below.
> 
> for (i in 1:100)
>   {
>     y <- rpois(i,lambda=10)
>     X0 <- seq(1,1,length=i)
>     X1 <- rnorm(i,mean=5,sd=10)
>     X2 <- rnorm(i,mean=17,sd=12)
>     X3 <- rnorm(i,mean=3, sd=24)
>     ind <- rep(1:5,20)
>   }
> 
> data100 <- cbind(y,X0,X1,X2,X3,ind)
> 
First, why the loop? For i in 1:99, this code is a waste
of computer time. The code should be:

  i <- 100
  y <- rpois(i,lambda=10)
  X0 <- seq(1,1,length=i)
  X1 <- rnorm(i,mean=5,sd=10)
  X2 <- rnorm(i,mean=17,sd=12)
  X3 <- rnorm(i,mean=3, sd=24)
  ind <- rep(1:5,20)
  data100 <- cbind(y,X0,X1,X2,X3,ind)
> but when i look at the data100 table, the y values now
> take the observation count. 
The y values should be the same as y. y is a (random)
array of integers.

Alberto Monteiro

Don't know what's wrong - it works:

 > data100
         y X0           X1           X2          X3 ind
   [1,] 11  1   2.79581511 -23.33335477 -33.6123061   1
   [2,]  8  1  21.43289242  21.52826214   3.8415209   2
   [3,]  6  1   6.18688631  21.51057247 -50.5547410   3
   [4,] 12  1  -5.95172686  13.74167916 -16.1798745   4
  <snip>

 > data100[y]
   [1]  9 10  8 18 10 10  9  7 11 11  7 10  9 14  7 18  9  7 10 10 18 10 
  9 11  9 10 11 11 11 10  8  9  8  7 18  9 11 15  7
  [40] 10  7  9  7 18 11 11 18 11 11 18  7 10 11  7 11 10 18  7  9  9  9 
  7  7  7 14 18 18 14 11 12 11  8 15  7  7  9 18 14
  [79] 10  7  7 12  7  7  9  8  7  8 11  7 15 18 18  7 15  7  7 11 11 10

These can pretty well be Poisson(10) variates... Remind that R is 
case-sensitive in names, y and Y is not the same.

However, I really hope you are not using the code given below since it 
is, well... very original... to generate something 100 times and to keep 
just the last value at the end.

Petr

Anup Nandialath napsal(a):
> Dear friends,
> 
> I have a basic question with R. I'm generating a set
> of random variables and then combining them using the
> cbind statement. The code for that is given below.
> 
> for (i in 1:100)
>   {
>     y <- rpois(i,lambda=10)
>     X0 <- seq(1,1,length=i)
>     X1 <- rnorm(i,mean=5,sd=10)
>     X2 <- rnorm(i,mean=17,sd=12)
>     X3 <- rnorm(i,mean=3, sd=24)
>     ind <- rep(1:5,20)
>   }
>   
> data100 <- cbind(y,X0,X1,X2,X3,ind)
> 
> but when i look at the data100 table, the y values now
> take the observation count. (ie) the data under Y is
> not the poisson random generates but the observation
> number. Hence the last vector (ind) does not have a
> header. Is there any way i can drop the number of
> observation counts being added into the matrix.
> 
> Thanks in advance for your help.
> 
> Sincerely
> 
> Anup
-- 
Petr Klasterecky
Dept. of Probability and Statistics
Charles University in Prague
Czech Republic