[R] Matrix multiplication by multple constants

[David Winsemius]

On Apr 20, 2012, at 4:57 AM, Dimitris Rizopoulos wrote:

> try this:
>
> x  <- 1:3
> y  <- matrix(1:12, ncol = 3, nrow = 4)
>
> y * rep(x, each = nrow(y))

Another way with a function specifically designed for that purpose:

sweep(y, 2, x, "*")

--  
David.

>
>
> I hope it helps.
>
> Best,
> Dimitris
>
>
> On 4/20/2012 10:51 AM, Vincy Pyne wrote:
>> Dear R helpers
>>
>> Suppose
>>
>> x<- c(1:3)
>>
>> y<- matrix(1:12, ncol = 3, nrow = 4)
>>
>>> y
>>      [,1] [,2] [,3]
>> [1,]    1    5    9
>> [2,]    2    6   10
>> [3,]    3    7   11
>> [4,]    4    8   12
>>
>> I wish to multiply 1st column of y by first element of x i.e. 1,  
>> 2nd column of y by 2nd element of x i.e. 2 an so on. Thus the  
>> resultant matrix should be like
>>
>>> z
>>
>>      [,1]   [,2]    [,3]
>>
>> [1,]    1    10    27
>>
>> [2,]    2    12    30
>>
>> [3,]    3    14    33
>>
>> [4,]    4    16    36
>>
>>
>> When I tried simple multiplication like x*y, y is getting  
>> multiplied column-wise
>>
>>> x*z
>>       [,1] [,2] [,3]
>> [1,]    1    5    9
>> [2,]    4   12   20
>> [3,]    9   21   33
>> [4,]   16   32   48
>>
>>
>> Kindly guide
>>
>> Regards
>>
>> Vincy
>>
>> 	[[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.
>
> -- 
> Dimitris Rizopoulos
> Assistant Professor
> Department of Biostatistics
> Erasmus University Medical Center
>
> Address: PO Box 2040, 3000 CA Rotterdam, the Netherlands
> Tel: +31/(0)10/7043478
> Fax: +31/(0)10/7043014
> Web: http://www.erasmusmc.nl/biostatistiek/
>
> ______________________________________________
> 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.

David Winsemius, MD
West Hartford, CT