# [R] Maximum of Maximum

Bert Gunter gunter.berton at gene.com
Fri Jan 10 22:13:34 CET 2014

```... In fact, on my computer, the pmax construction took longer. I
would guess that's due to the data.frame construction. Nevertheless,
the comment is still germane.

Cheers,
Bert

Bert Gunter
Genentech Nonclinical Biostatistics
(650) 467-7374

"Data is not information. Information is not knowledge. And knowledge
is certainly not wisdom."
H. Gilbert Welch

On Fri, Jan 10, 2014 at 1:03 PM, Bert Gunter <bgunter at gene.com> wrote:
> It probably doesn't make much difference in this small example, but
> maybe it's worth noting that **if possible** (it typically is not),
> things can be speeded up by generating all the random numbers at once
> then applying a vectorized operation to the entire ensemble. In this
> case, this becomes:
>
> ran <- do.call(pmax,data.frame(matrix(rnorm(1e6),nr=1000)))
>
> pmax() is the vectorized operation. The do.call(...,data.frame(..)))
> construction must be used to satisfy the argument list requirements
> for pmax and do.call.
>
> Cheers,
> Bert
>
>
> Bert Gunter
> Genentech Nonclinical Biostatistics
> (650) 467-7374
>
> "Data is not information. Information is not knowledge. And knowledge
> is certainly not wisdom."
> H. Gilbert Welch
>
>
>
>
> On Fri, Jan 10, 2014 at 12:31 PM, arun <smartpink111 at yahoo.com> wrote:
>> Hi,
>>
>> May be this helps:
>> set.seed(42)
>>  vec1 <- sapply(1:1000,function(x) max(rnorm(1000,0,1)))
>> #or
>> set.seed(42)
>>  vec2 <- replicate(1000,max(rnorm(1000,0,1)))
>> identical(vec1,vec2)
>> #[1] TRUE
>>
>> set.seed(598)
>> res <- sample(vec1,100,replace=FALSE)
>>
>>  max(res)
>> #[1] 4.408794
>> A.K.
>>
>> Hello I need some help in programming:
>>
>> I want to after take a rnorm(1000,0,1) sample want to save the
>> max of it in a vector, this was difficult to me, then I need to repeat
>> this process 1000 times, so I shall have 1000 maximum from the normal of
>>  samples of size 1000.
>> Then I want to sample from this maximum series a new sample, this time of size 100.
>>
>> I drive a programm:
>>
>> sample<-rnorm(1000,0,1)
>> for(i in 1:length(sample)){
>>    maxim<-vector(mode="numeric",length(sample))
>>    maxim[i]<-max(sample)
>> }
>>
>> then my result was a vector with n-1 zeroes and the last one
>> value was a maximum. I think it took the last value, but I don't know
>> how to repair it.
>>
>> I need most help, thanks
>>
>>
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