[R] Matrix element-by-element multiplication
R. Michael Weylandt
michael.weylandt at gmail.com
Sun Nov 6 05:21:34 CET 2011
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 <syen at utk.edu> wrote:
> My earlier attempt
>
> dp <- v*b
>
> did not work. Then,
>
> dp <- c(v)*b
>
> worked.
>
> 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 <syen at 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
>>
>>
>> --
>> Steven T. Yen, Professor of Agricultural Economics
>> The University of Tennessee
>> http://web.utk.edu/~syen/
>> [[alternative HTML version deleted]]
>>
>> ______________________________________________
>> R-help at 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.
>>
>
> --
> Steven T. Yen, Professor of Agricultural Economics
> The University of Tennessee
> http://web.utk.edu/~syen/
More information about the R-help
mailing list