R help - Nov 2011 - Matrix element-by-element multiplication

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]]

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.
>

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/

It looks like pdf is not a "scalar" (that term actually has no meaning
in R but I know what you mean) but is rather a 1x1 matrix, as attested by the
fact it has dimensions. If you give dnorm() a matrix it will return one, as it
did here.

Perhaps you should look at the is.matrix() and as.vector() functions rather than
abusing a side-effect of c(), which makes it much more difficult to see R's
internal logic, which, while quirky, is useful at the end of the day.

Michael

PS - It's good form to cc the list at each step so others can follow along
and contribute when I say something wrong. It also helps you get quicker
answers.

On Nov 6, 2011, at 1:06 AM, Steven Yen <syen@utk.edu> wrote:
> I am trying to multiply what I know is a scalar (pdf(xb)) to a column
vector of coefficient (bb).
> In the following, pdf is a scalar and bb is 5 x 1. I first show what worked
and then what did not work.
> If my pdf is a scalar, why would I need c(pdf) to be able to pre-multiply
it by a 5 x 1 vector?
> 
> ---
> 
> > x      <- as.matrix(colMeans(x))
> > xb     <- t(x)%*%bb
> > pdf    <- dnorm(xb)
> 
> > dim(bb)
> [1] 5 1
> 
> > 
> > cpdf  <- c(pdf)
> > dim(cpdf)
> NULL
> > cpdf
> [1] 0.304201
> > (dphat <- cpdf*bb)
>                    [,1]
> (Intercept)  0.32744753
> xrage       -0.00599225
> xryr         0.01758431
> xrrate      -0.08217250
> xrrel       -0.05695434
> > 
> > pdf    <- dnorm(xb)
> > dim(pdf)
> [1] 1 1
> > pdf
>          [,1]
> [1,] 0.304201
> > (dphat <-  pdf*bb)
> Error in pdf * bb : non-conformable arrays
> > 
> 
> At 12:21 AM 11/6/2011, you 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 <syen@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@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@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/
> --
> Steven T. Yen, Professor of Agricultural Economics
> The University of Tennessee
> http://web.utk.edu/~syen/
	[[alternative HTML version deleted]]

Hello Steven,

It looks like, there is no in-built function that can do GAUSS ".*"
element-wise multiplication.
Now, if you want to make the desired computations in R, it is actually
preatty straightforward.
> a<-c(1,2,3)
> b<-matrix(rep(1:9,1),3,3,byrow=TRUE)
> a*b
That, should work fine. But, suppose that for some reason you have following
situation, which can make you trip for hours of sleepless nights. That is,
you have a matrix "b", where number of columns equal to number of
columns of
your vector "a". That is
> b<-matrix(rep(1:9,1),3,3,byrow=TRUE);b
     [,1] [,2] [,3]
[1,]    1    2    3
[2,]    4    5    6
[3,]    7    8    9
> a <- matrix(rep(1:3,1),1,3,byrow=TRUE)
     [,1] [,2] [,3]
[1,]    1    2    3

If you try to do elementwise multilication, i.e., of those
two
> b*a
You get an error that they are not comfomable, that is why, you have to
write your own function (here, 
I just write the for-loop):
> for ( i in 1:3 ) {
     foo[ ,i] = ( foo[ ,i] * bar[1,i] ) ;
   }
       [,1] [,2] [,3]
[1,]    1    4    9
[2,]    4   10   18
[3,]    7   16   27

I hope that this helped
Serge Boris Nesterenko
CEO 50 Pence Music Production
https://www.linkedin.com/in/sergenesterenko



--
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Sent from the R help mailing list archive at Nabble.com.

On 30/09/15 12:49, waddawanna wrote:
> Hello Steven,
>
> It looks like, there is no in-built function that can do GAUSS
".*"
> element-wise multiplication.
> Now, if you want to make the desired computations in R, it is actually
> preatty straightforward.
>
>> a<-c(1,2,3)
>> b<-matrix(rep(1:9,1),3,3,byrow=TRUE)
>> a*b
>
> That, should work fine. But, suppose that for some reason you have
following
> situation, which can make you trip for hours of sleepless nights. That is,
> you have a matrix "b", where number of columns equal to number of
columns of
> your vector "a". That is
>
>> b<-matrix(rep(1:9,1),3,3,byrow=TRUE);b
>       [,1] [,2] [,3]
> [1,]    1    2    3
> [2,]    4    5    6
> [3,]    7    8    9
>
>> a <- matrix(rep(1:3,1),1,3,byrow=TRUE)
>       [,1] [,2] [,3]
> [1,]    1    2    3
>
> If you try to do elementwise multilication, i.e., of those two
>> b*a
>
> You get an error that they are not comfomable, that is why, you have to
> write your own function (here,
> I just write the for-loop):
>> for ( i in 1:3 ) {
>       foo[ ,i] = ( foo[ ,i] * bar[1,i] ) ;
>     }
>         [,1] [,2] [,3]
> [1,]    1    4    9
> [2,]    4   10   18
> [3,]    7   16   27
>
> I hope that this helped.

(1) You're making heavy weather by using rep() totally unnecessarily.


(2) The example you give can be done much more succinctly; for-loops
are unnecessary:

    t(as.vector(a)*t(b))

(3) Please don't post to R-help via nabble (WTF ever that is).  It 
messes up everything.

cheers,

Rolf Turner

-- 
Technical Editor ANZJS
Department of Statistics
University of Auckland
Phone: +64-9-373-7599 ext. 88276

On Sep 29, 2015, at 4:49 PM, waddawanna wrote:
> Hello Steven,
> 
> It looks like, there is no in-built function that can do GAUSS
".*"
> element-wise multiplication.
> Now, if you want to make the desired computations in R, it is actually
> preatty straightforward.
> 
>> a<-c(1,2,3)
>> b<-matrix(rep(1:9,1),3,3,byrow=TRUE)
>> a*b
> 
> That, should work fine. But, suppose that for some reason you have
following
> situation, which can make you trip for hours of sleepless nights. That is,
> you have a matrix "b", where number of columns equal to number of
columns of
> your vector "a". That is
> 
>> b<-matrix(rep(1:9,1),3,3,byrow=TRUE);b
>     [,1] [,2] [,3]
> [1,]    1    2    3
> [2,]    4    5    6
> [3,]    7    8    9
> 
>> a <- matrix(rep(1:3,1),1,3,byrow=TRUE)
>     [,1] [,2] [,3]
> [1,]    1    2    3
> 
> If you try to do elementwise multilication, i.e., of those two
>> b*a
> 
> You get an error that they are not comfomable,
You should not have gotten that error with either `*` or `%*%`.
> that is why, you have to
> write your own function (here, 
> I just write the for-loop):
>> for ( i in 1:3 ) {
>     foo[ ,i] = ( foo[ ,i] * bar[1,i] ) ;
>   }
>       [,1] [,2] [,3]
> [1,]    1    4    9
> [2,]    4   10   18
> [3,]    7   16   27
You were expecting c(1,2,3) to be a row-vector. That leads to disappointment. If
anything it will be a column-vector.

Notice .... no error:
> a*b
     [,1] [,2] [,3]
[1,]    1    2    3
[2,]    8   10   12
[3,]   21   24   27


You really wanted to sweep that vector
> sweep(b, 1,a,'*')   # Sweeping by rows is same a multiplying by
recycle column vector
     [,1] [,2] [,3]
[1,]    1    2    3
[2,]    8   10   12
[3,]   21   24   27
> sweep(b, 2, a, '*')  # You wanted to "sweep" across
columns
     [,1] [,2] [,3]
[1,]    1    4    9
[2,]    4   10   18
[3,]    7   16   27

-- 

David Winsemius
Alameda, CA, USA