[R] efficiency with "%*%"

[Philippe Grosjean]

Excellent, but...

 > x <- rnorm(1000000)
 > y <- rnorm(1000000)
 > system.time(x%*%y)
[1] 0.03 0.00 0.03   NA   NA
 > system.time(sum(x*y))
[1] 0.05 0.00 0.04   NA   NA
 > system.time(crossprod(x, y))
[1]  0  0  0 NA NA

So, to paraphrase a well-known contributor on this mailing list:
"Excellent! So, what did you decided to do during the next 30 
milliseconds you will save by using crossprod() instead of x%*%y?
(joke)

Best,

Philippe Grosjean

P.S.: Uwe, perhaps you should consider buying a faster computer, isn't 
it? :-()

Uwe Ligges wrote:
> dimitrijoe at ipea.gov.br wrote:
> 
> 
>>Hi,
>>
>>x and y are (numeric) vectors. I wonder if one of the following is more
>>efficient than the other:
>>
>>x%*%y
>>
>>or
>>
>>sum(x*y)
>>?
> 
> 
> I'd try
> 
>    x <- rnorm(1000000)
>    y <- rnorm(1000000)
>    system.time(x%*%y)
>    system.time(sum(x*y))
> 
> and finally (hint, hint!):
> 
>    system.time(crossprod(x, y))
> 
> Uwe Ligges
> 
> 
> 
>>Thanks,
>>Dimitri Szerman
>>
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> 
> 
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