Why this works does not become clear until you actually pay attention to how
matrices are laid out in memory as a vector, and how vector replication works.
Those ideas are not that difficult to learn, but they feel different than in
other languages (e.g. matlab) and they make a huge difference when you want to
speed things up. Read the appropriate section in the Introduction to R document
that comes with R until you see what is happening, and ask for clarification if
you are still lost.
--
Sent from my phone. Please excuse my brevity.
On February 21, 2017 9:00:59 AM PST, William Dunlap via R-help <r-help at
r-project.org> wrote:>> Mat * c(3, 1, 0.5)
> [,1] [,2] [,3]
>[1,] 3.0 6 9.0
>[2,] 4.0 5 6.0
>[3,] 3.5 4 4.5
>
>
>Bill Dunlap
>TIBCO Software
>wdunlap tibco.com
>
>
>On Tue, Feb 21, 2017 at 8:23 AM, <ac.dasilva at ulg.ac.be> wrote:
>> If we have the following matrix:
>>
>> Mat<-matrix(1:9, byrow=TRUE, nrow=3)
>> Mat
>>
>> [,1] [,2] [,3]
>> [1,] 1 2 3
>> [2,] 4 5 6
>> [3,] 7 8 9
>>
>> I would like to have each row multiplied by a different number.
>> So I would like row 1 multiplied by 3, row2 by 1 and row3 by 0.5
>> Which would give:
>>
>> [,1] [,2] [,3]
>> [1,] 3 6 9
>> [2,] 4 5 6
>> [3,] 3.5 4 4.5
>>
>>
>> Whatever I try, I always obtain
>> [,1] [,2] [,3]
>> [1,] 3 2 1.5
>> [2,] 12 5 3.0
>> [3,] 21 8 4.5
>>
>> Which corresponds to the columns multiplied by the factors
>>
>> Could anyone help we to get the proper result ?
>> Best, Anne-Christine da Silva
>>
>> ______________________________________________
>> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
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>> PLEASE do read the posting guide
>http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>
>______________________________________________
>R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
>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.