On Nov 6, 2011, at 12:21 AM, R. Michael Weylandt wrote:
There are a few (nasty?) side-effects to c(), one of which is
stripping a matrix of its dimensionality. E.g.,
x <- matrix(1:4, 2)
c(x)
[1] 1 2 3 4
So that's probably what happened to you. R has a somewhat odd feature
of not really considering a pure vector as a column or row vector but
being willing to change it to either:
e.g.
y <- 1:2
x %*% y
y %*% x
y %*% y
while matrix(y) %*% x throws an error, which can also trip folks up.
You might also note that x * y and y*x return the same thing in this
problem.
Getting back to your problem: what are v and b and what are you hoping
to get done? Specifically, what happened when you tried v*b (give the
exact error message). It seems likely that they are non-conformable
matrices, but here non-conformable for element-wise multiplication
doesn't mean the same thing as it does for matrix multiplication.
E.g.,
x <- matrix(1:4,2)
y <- matrix(1:6,2)
dim(x)
[1] 2 2
dim(y)
[1] 2 3
x * y -- here R seems to want matrices with identical dimensions, but
i can't promise that.
x %*% y does work.
Hope this helps and yes I know it can seem crazy at first, but there
really is reason behind it at the end of the tunnel,
Michael
On Sun, Nov 6, 2011 at 12:11 AM, Steven Yen <s...@utk.edu> wrote:
My earlier attempt
dp <- v*b
did not work.
Because the dimensions did not work. dim(v)[1] (the rows) did not
equal dim(b)[2] (the columns) since b did not have a dimension.
Then,
dp <- c(v)*b
worked.
It worked because of argument recycling. It did not give you a matrix
result, however, because of what Michael said. c() turns a matrix into
a vector, which it was all along anyway.
Here's an example of argument recycling:
> c(1, 2, 3) * 1:12
[1] 1 4 9 4 10 18 7 16 27 10 22 36
The 1,2,3 vector gets implicitly lengthened as would have happened
with rep(c(1,2,3), 4) and then
--
David.
Confused,
Steven
At 09:10 PM 11/4/2011, you wrote:
Did you even try?
a <- 1:3
x <- matrix(c(1,2,3,2,4,6,3,6,9),3)
a*x
[,1] [,2] [,3]
[1,] 1 2 3
[2,] 4 8 12
[3,] 9 18 27
Michael
On Fri, Nov 4, 2011 at 7:26 PM, Steven Yen <s...@utk.edu> wrote:
is there a way to do element-by-element multiplication as in Gauss
and MATLAB, as shown below? Thanks.
---
a
1.0000000
2.0000000
3.0000000
x
1.0000000 2.0000000 3.0000000
2.0000000 4.0000000 6.0000000
3.0000000 6.0000000 9.0000000
a.*x
1.0000000 2.0000000 3.0000000
4.0000000 8.0000000 12.000000
9.0000000 18.000000 27.000000
--
David Winsemius, MD
West Hartford, CT
______________________________________________
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
