On Fri, Jul 23, 2010 at 11:11 AM, aegea <gche...@gmail.com> wrote:
>
> Thanks in advance!
>
> A=c(1, 2,3)
> B=c (9, 10, 11, 12)
>
> I want to get C=c(1*9, 1*10, 1*11, 1*12, ....., 3*9, 3*10, 3*11, 3*12)?
> C is still a vector with 12 elements
> Is there a way to do that?
Here are yet a few more. The first one is the only one so far that
uses a single function and the last two are slight variations of ones
already posted.
kronecker(A, B)
c(tcrossprod(B, A))
c(outer(B, A))
c(B %o% A)
Here is a speed comparison. The fastest are as.matrix, %outer% and
%o% . They are so close that random fluctuations might easily change
their order and since %o% involves the least keystrokes that one might
be a good overall choice. Although not among the fastest the
kronecker solution is the simplest since it only involves a single
function call so it might be preferred on that count.
> A <- B <- 1:400
> out <- benchmark(
+ as.matrix = c(as.matrix(B) %*% A),
+ crossprod = c(tcrossprod(B, A)),
+ outer = c(outer(B, A)),
+ o = c(B %o% A),
+ kronecker = kronecker(A, B),
+ touter = as.vector(t(outer(A, B))))
> out[order(out$relative), ]
test replications elapsed relative user.self sys.self
user.child sys.child
1 as.matrix 100 0.92 1.000000 0.62 0.28
NA NA
3 outer 100 0.93 1.010870 0.59 0.35
NA NA
4 o 100 0.94 1.021739 0.66 0.28
NA NA
2 crossprod 100 1.11 1.206522 0.67 0.43
NA NA
5 kronecker 100 1.45 1.576087 1.25 0.21
NA NA
6 touter 100 1.84 2.000000 1.40 0.43
NA NA
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