[R] avoid a loop

[Martin Morgan]

Gabor Grothendieck wrote:
> Try this:
> 
>> sapply(1:n, function(i) sum(abs(outer(a, b, "-")-i)==0))
> [1] 10 10 10 10  9

abs(outer(a, b, "-") - i) == 0 ==> outer(a, b, "-") == i.

sum(outer(a, b, "-") == i) asks how many times i is an element of 
outer(a, b, "-"). This is

tabulate(outer(a, b, "-"), n)

I think, anyway.

Martin

> 
> 
> On Thu, May 28, 2009 at 5:45 PM, KARAVASILIS GEORGE <gkaravas at ee.duth.gr> wrote:
>> Hello, R users.
>> I have the following code:
>>
>> a=1:10
>> b=-3:15
>> n=5
>> x <- rep(0,n)
>> for (i in 1:n) x[i] <- sum( outer(a,b, function(s,t)  abs(a-b-i)==0) )
>>
>> Can someone tell me if I could avoid the for command?
>>
>> Thank you in advance.
>>
>> ______________________________________________
>> R-help at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.


-- 
Martin Morgan
Computational Biology / Fred Hutchinson Cancer Research Center
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