R help - Jun 2010 - Question about avoid the for loop

Dear R-helpers,

I would like to generate a binary random variable within a stratum's
stratum. Here is a simple example.


## x is the first level strata index, here I have 3 strata.
x=c(rep(1,5), rep(2,5), rep(3,5))

## within x, there is a second strata indexed by t=0 and t=1
t=rep(c(0,0,1,1,1),3)


## and within strata i and t=0 and t=1, I generate the random binomial
variable respectively, and save in y
y=rep(NA, length(x))
for (i in 1:3)
{
y[(x==i)&(t==0)]=rbinom(2, 1, 0.2)
y[(x==i)&(t==1)]=rbinom(3, 1, 0.8)
}


My question: is there any way to avoid the for loop, since I have the first
level strata has thousands of strata. (Within each x stratum, the t only has
2 levels, 0 and 1 )

Thanks for any help!

Carrie

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Hi Carrie,

Here are two options:

# Option 1
d <- data.frame(x, t)
y <- with(d, ifelse(t == 0, rbinom(2, 1, 0.2), rbinom(3, 1, 0.8)))
y

# Option 2  -- more general case, e.g. you do not know
#  how many 0's and 1's you have within each strata
spd <- with(d, split(d, x))
do.call(c, lapply(spd, function(comp)
                with(comp, ifelse(t == 0, rbinom(sum(t==0), 1, 0.2),
rbinom(sum(t!=0), 1, 0.8)))))

HTH,
Jorge


On Thu, Jun 3, 2010 at 11:49 AM, Carrie Li <> wrote:
> Dear R-helpers,
>
> I would like to generate a binary random variable within a stratum's
> stratum. Here is a simple example.
>
>
> ## x is the first level strata index, here I have 3 strata.
> x=c(rep(1,5), rep(2,5), rep(3,5))
>
> ## within x, there is a second strata indexed by t=0 and t=1
> t=rep(c(0,0,1,1,1),3)
>
>
> ## and within strata i and t=0 and t=1, I generate the random binomial
> variable respectively, and save in y
> y=rep(NA, length(x))
> for (i in 1:3)
> {
> y[(x==i)&(t==0)]=rbinom(2, 1, 0.2)
> y[(x==i)&(t==1)]=rbinom(3, 1, 0.8)
> }
>
>
> My question: is there any way to avoid the for loop, since I have the first
> level strata has thousands of strata. (Within each x stratum, the t only
> has
> 2 levels, 0 and 1 )
>
> Thanks for any help!
>
> Carrie
>
>        [[alternative HTML version deleted]]
>
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> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
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