R help - Jun 2006 - A coding question

Dear List:

I have the follow code:

y <- replicate(10,replicate(8,sum(rnorm(rpois(1,5)))))

Now I need to apply the following condition to _every_ randomly generated
Normal number in the code above:

x - max(0,x-15) + max(0,x-90), where x represents the individual Normal
numbers.

In other words, the said condition needs to be applied before
replicate(...(replicate(...(sum(...))) takes place.

Any help would be greatly appreciated.


platform i386-pc-mingw32
arch i386
os mingw32
system i386, mingw32
status
major 2
minor 2.1
year 2005
month 12
day 20
svn rev 36812
language R

xpRt.wannabe wrote:
> Dear List:
> 
> I have the follow code:
> 
> y <- replicate(10,replicate(8,sum(rnorm(rpois(1,5)))))
> 
> Now I need to apply the following condition to _every_ randomly generated
> Normal number in the code above:
> 
> x - max(0,x-15) + max(0,x-90), where x represents the individual Normal
> numbers.
> 
> In other words, the said condition needs to be applied before
> replicate(...(replicate(...(sum(...))) takes place.
> 
> Any help would be greatly appreciated.

y <- replicate(10, {
         rp <- rpois(8, 5)
         mysum <- sapply(rp, function(x) {
             x <- rnorm(x)
             x <- x - max(0, x-15) + max(0, x-90)
             sum(x)
         })
      })
> 
> platform i386-pc-mingw32
> arch i386
> os mingw32
> system i386, mingw32
> status
> major 2
> minor 2.1
> year 2005
> month 12
> day 20
> svn rev 36812
> language R
> 
> ______________________________________________
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> PLEASE do read the posting guide!
http://www.R-project.org/posting-guide.html

Uwe Ligges <ligges <at> statistik.uni-dortmund.de> writes:
> 
> xpRt.wannabe wrote:
> 
> > y <- replicate(10,replicate(8,sum(rnorm(rpois(1,5)))))
> > 
> > x - max(0,x-15) + max(0,x-90), where x represents the individual
Normal
> > numbers.
> 
> y <- replicate(10, {
>          rp <- rpois(8, 5)
>          mysum <- sapply(rp, function(x) {
>              x <- rnorm(x)
>              x <- x - max(0, x-15) + max(0, x-90)
>              sum(x)
>          })
>       })
> 
  I think this can be boiled down a bit further.

x-max(0,x-15)+max(0,x-90)

if x>90:        x-(x-15)+(x-90) = x+15-90=x-75
if 15<x<90      x-(x-15)+0      = 15
if x<15         x-0+0           = x

therefore

tmpf <- function() {
  x <- rnorm(rpois(1,5))
  sum(ifelse(x>90,x-75,pmin(x,15)))
}

replicate(10,replicate(8,tmpf()))

(you could also generate 80 values and then break them
 up into segments of 8)

  Ben Bolker

Uwe and Ben,

Thank you both for your help.

To me, both sets of code seem to do the job and should produce the
same results.  However, as a test I inserted set.seed( ) as follows.
Unless I put set.seed( ) in the wrong lines, the results produced by
both sets of code turn out to be different.  I am baffled.

y <- replicate(10, {
        set.seed(123)
        rp <- rpois(8, 5)
        mysum <- sapply(rp, function(x) {
            set.seed(123)
            x <- rnorm(x)
            x <- x - max(0, x-15) + max(0, x-90)
            sum(x)
        })
     })

##

tmpf <- function() {
set.seed(123)
x <- rnorm(rpois(1,5))
sum(ifelse(x>90,x-75,pmin(x,15)))
}
replicate(10,replicate(8,tmpf()))

On 6/2/06, Uwe Ligges <ligges at statistik.uni-dortmund.de>
wrote:
> xpRt.wannabe wrote:
>
> > Dear List:
> >
> > I have the follow code:
> >
> > y <- replicate(10,replicate(8,sum(rnorm(rpois(1,5)))))
> >
> > Now I need to apply the following condition to _every_ randomly
generated
> > Normal number in the code above:
> >
> > x - max(0,x-15) + max(0,x-90), where x represents the individual
Normal
> > numbers.
> >
> > In other words, the said condition needs to be applied before
> > replicate(...(replicate(...(sum(...))) takes place.
> >
> > Any help would be greatly appreciated.
>
>
> y <- replicate(10, {
>         rp <- rpois(8, 5)
>         mysum <- sapply(rp, function(x) {
>             x <- rnorm(x)
>             x <- x - max(0, x-15) + max(0, x-90)
>             sum(x)
>         })
>      })

xpRt.wannabe wrote:
> Uwe and Ben,
> 
> Thank you both for your help.
> 
> To me, both sets of code seem to do the job and should produce the
> same results.  However, as a test I inserted set.seed( ) as follows.
> Unless I put set.seed( ) in the wrong lines, the results produced by
> both sets of code turn out to be different.  I am baffled.
> y <- replicate(10, {
>        set.seed(123)
So you reset the RNG 10 times, makes no sense, move set.seed before the 
first replicate().

>        rp <- rpois(8, 5)
You get 8 (!) different values here (in contrast to the code below).
>        mysum <- sapply(rp, function(x) {
>            set.seed(123)
And again. Makes no sense either.
>            x <- rnorm(x)
>            x <- x - max(0, x-15) + max(0, x-90)
>            sum(x)
>        })
>     })
> 
> ##
> 
> tmpf <- function() {
> set.seed(123)
Here, you reset  80 times, each time you get the same value for rpois().
> x <- rnorm(rpois(1,5))
> sum(ifelse(x>90,x-75,pmin(x,15)))
> }
> replicate(10,replicate(8,tmpf()))

You cannot compare the results of both code fragments with set.seed() 
due to the different stucture when which random number is generated.
(even permutation of generation of normal and poisson distributed random 
numbers).

Uwe Ligges

> On 6/2/06, Uwe Ligges <ligges at statistik.uni-dortmund.de> wrote:
> 
>> xpRt.wannabe wrote:
>>
>> > Dear List:
>> >
>> > I have the follow code:
>> >
>> > y <- replicate(10,replicate(8,sum(rnorm(rpois(1,5)))))
>> >
>> > Now I need to apply the following condition to _every_ randomly 
>> generated
>> > Normal number in the code above:
>> >
>> > x - max(0,x-15) + max(0,x-90), where x represents the individual
Normal
>> > numbers.
>> >
>> > In other words, the said condition needs to be applied before
>> > replicate(...(replicate(...(sum(...))) takes place.
>> >
>> > Any help would be greatly appreciated.
>>
>>
>> y <- replicate(10, {
>>         rp <- rpois(8, 5)
>>         mysum <- sapply(rp, function(x) {
>>             x <- rnorm(x)
>>             x <- x - max(0, x-15) + max(0, x-90)
>>             sum(x)
>>         })
>>      })