On Wed, Mar 07, 2012 at 03:14:05PM -0500, Alexander Shenkin wrote:
> Hello,
>
> I need to take a dot product of each row of a dataframe and a vector.
> The number of columns will be dynamic. The way I've been doing it so
> far is contorted. Is there a better way?
>
> dotproduct <- function(dataf, v2) {
> apply(t(t(as.matrix(a)) * v2),1,sum) #contorted!
> }
>
> df = data.frame(a=c(1,2,3),b=c(4,5,6))
> vec = c(4,5)
> dotproduct(df, vec)
Hi.
If i understand correctly, then the following should
be equivalent
as.matrix(df) %*% cbind(vec)
[,1]
[1,] 24
[2,] 33
[3,] 42
Hope this helps.
Petr Savicky.
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