[BioC] script line to multiply a vector by another vector or matrix

[Patrick Aboyoun]

Carol,
I think if you write down the rules to how you would like your operation 
to behave, you will find the solution and if not, we could help you out. 
I thought I could decipher what the rules were but the operation

a1 = c(1)
a2 = c(1,2)
res = a1*a2 = [3]
 sum(c(1)*c(1,2)) to get 3
here, %*% is not of help


got the Sesame Street song "One of these things is not like the others" 
stuck in my head.


Patrick


carol white wrote:
> Hi,
> I
> want to multiply a vector (1st argument) by another vector or a matrix
> (2nd argument) depends if a column or a row of a matrix or a subset of
> a matrix is taken. The first argument presents a coefficient vector (of
> 1 or more elements) that will be multiplied by all elements of the 2nd
> argument. Therefore, the final product (multiplication of the 2
> arguments) will be a vector of the length of the number of rows of the
> 2nd argument.
>
> I wanted to use %*% for all cases, either taking
> directly the 2nd argument or its tansposal but it doesn't work for all
> cases. Do I have to test the type of 2nd argument and write a different
> script lines or can I use a script line for all cases?
>
> for example, I will have the following different cases:
>
> a1 = c(1)
> a2 = c(2)
> res = a1*a2 = 2
> c(1)%*%c(2)
>     
>  [,1]
> [1,]    2
>
> a1 = c(1)
> a2 = c(1,2)
> res = a1*a2 = [3]
>  sum(c(1)*c(1,2)) to get 3
> here, %*% is not of help
>
> a1 = c(1,2)
> a2 = c(2,1)
> res = 4
> c(1,2)%*%c(2,1)
> so a1%*%a2 would work
>
> a1 = c(1,2)
> a2 = rbind(c(1,2), c(2,1))
> res = [5 4]
> a1%*%a2
>      [,1] [,2]
> [1,]    5    4
>
>   a1 = c(1,2,3)
>  a2 = rbind(c(1,2,3), c(2,1,3))
> a1%*%t(a2)
>      [,1] [,2]
> [1,]   14   13
>
> etc
>
>
>
>       
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>
>   
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