[R] Effective code for 2 vector multiplication?

[Moshe Olshansky]

You can use matrix by vector multiplication:

m <- as.matrix(POPULATION)
beta <- as.numeric(beta.vector)
y <- m %*% beta
POPULATION <- cbind(POPULATION,y)

--- Dimitri Liakhovitski <ld7631 at gmail.com> wrote:

> Hello!
> 
> I have a data frame POPULATION populated with
> numeric values such that
> dim(POPULATION) are: 100,000 (rows) and 3 (columns).
> 
> Also, I have a vector beta.vector that has 3
> elements (all numeric values).
> 
> I want to create a new variable Y (a new column) in
> POPULATION such
> that for each row of POPULATION, the value of Y
> equals the product of
> 2 vectors: 3 values of the corresponding row of
> POPULATION times
> beta.vector.
> 
> Here is the code I wrote:
> 
> POPULATION$Y<-sapply(as.list(1:nrow(POPULATION)),
> function(x) {
> x2<-as.numeric(POPULATION[x,]) %*%
> as.numeric(beta.vector)
> return(x2)
> } )
> 
> It calculates what I need and creates POPULATION$Y
> BUT - it takes 50
> seconds (!!!)
> My question: is there a more effective (faster) way
> of doing what I am
> trying to do?
> 
> Thanks a lot!
> Dimitri
> 
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