Sorry - I just noticed you actually have an error in your code: you had
parentheses everywhere they were not needed and I overlooked you had not put
them where they actually are needed. It has to be for (i in 1:(m-1)) ..., not
as you wrote. I'm sure you'll understand the difference.
d <- numeric(m-1)
for (i in 1:(m-1)) {
d[i] <- n - sum(x[1:i]) - i
}
B.
On Oct 25, 2015, at 8:13 AM, Boris Steipe <boris.ste...@utoronto.ca> wrote:
> If this code is slow it is not because you are using loops, but because you
> are dynamically building your vectors and lists and their size needs to
> change with each iteration causing significant unnecessary computational
> overhead. If you simply do something like
>
> d <- numeric(m-1)
> for (i in 1:m-1) {
> d[i] <- n - sum(x[1:i]) - i
> }
>
> for all of your loops, you will see already see very significant speedup. (If
> you look at my code formatting, and compare it with your own you may also
> benefit.) The bottom line: the point is not to avoid for-loops, but to speed
> up your code.
>
> Nb. if you want to avoid loops for some aesthetic reason, read about apply()
> and its siblings, and experiment with it. Of course, internally an apply()
> statement uses loops...
>
> NNb: Do you know how to profile your code? How do you know which part of your
> code is actually slowing it down?
>
>
>
> B.
>
>
>
>
> On Oct 25, 2015, at 6:42 AM, Maram SAlem <marammagdysa...@gmail.com> wrote:
>
>> Hi All,
>>
>> I wonder if I can avoid the for() loop in any of the following loops.These
>> loops are a part of a larger code which I'm trying to accelerate.
>>
>> n=6
>> m=4
>> x<-c(0,1,1)
>>
>> 1st loop
>>
>> for (i in 1:m-1)
>> {
>> d[i]<- n- (sum(x[(1):(i)])) - i
>> }
>> e<- n*(prod(d))
>>
>>
>> 2nd loop
>>
>> LD<-list()
>> for (i in 1:(m-1))
>> {
>> LD[[i]]<-seq(0,x[i],1)
>> }
>>
>> LD[[m]]<-seq(0,(n-m-sum(x)),1)
>> LED<-expand.grid (LD)
>> LED<-as.matrix(LED)
>>
>>
>> 3rd loop
>>
>> for (i in 1:(m-1))
>>
>> {
>>
>> h[i]<- choose(x[i],LED[j,i])
>>
>> }
>>
>>
>>
>> 4th loop
>>
>>
>> for (i in 1:(m-1))
>>
>> {
>>
>> lm[i]<-(sum(LED[j,1:i])) + i
>>
>> }
>>
>>
>> I appreciate if anyone has any suggestions or references.
>>
>>
>> Thanks in advance.
>>
>>
>> Maram Salem
>>
>> [[alternative HTML version deleted]]
>>
>> ______________________________________________
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>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>
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