My goodness!> x %*% diag(y)[,1] [,2] [1,] 2 12 [2,] 4 15 [3,] 6 18 will do. -- Bert Bert Gunter "The trouble with having an open mind is that people keep coming along and sticking things into it." -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip ) On Thu, Nov 3, 2016 at 2:33 PM, Sarah Goslee <sarah.goslee at gmail.com> wrote:> Like this? > >> sweep(x, 2, y, "*") > [,1] [,2] > [1,] 2 12 > [2,] 4 15 > [3,] 6 18 >> > > > On Thu, Nov 3, 2016 at 5:05 PM, Dimitri Liakhovitski > <dimitri.liakhovitski at gmail.com> wrote: >> Hello! >> >> I have a matrix x and a vector y: >> >> x <- matrix(1:6, ncol = 2) >> y <- c(2,3) >> >> I need to multiply the first column of x by 2 (y[1]) and the second >> column of x by 3 (y[2]). >> >> Of course, I could do this - but it's column by column: >> >> x[,1] <- x[,1] * y[1] >> x[,2] <- x[,2] * y[2] >> x >> >> Or I could repeat each element of y and multiply two matrices - that's better: >> >> rep.row<-function(x,n){ >> matrix(rep(x,each=n),nrow=n) >> } >> y <- rep.row(y, nrow(x)) >> x * y >> >> However, maybe there is a more elegant r-like way of doing it? >> Thank you! >> >> -- >> Dimitri Liakhovitski >> > > -- > Sarah Goslee > http://www.functionaldiversity.org > > ______________________________________________ > 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.
Nice! Thanks a lot, everybody! Dimitri On Fri, Nov 4, 2016 at 10:35 AM, Bert Gunter <bgunter.4567 at gmail.com> wrote:> My goodness! > >> x %*% diag(y) > > [,1] [,2] > [1,] 2 12 > [2,] 4 15 > [3,] 6 18 > > will do. > > -- Bert > > > > Bert Gunter > > "The trouble with having an open mind is that people keep coming along > and sticking things into it." > -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip ) > > > On Thu, Nov 3, 2016 at 2:33 PM, Sarah Goslee <sarah.goslee at gmail.com> wrote: >> Like this? >> >>> sweep(x, 2, y, "*") >> [,1] [,2] >> [1,] 2 12 >> [2,] 4 15 >> [3,] 6 18 >>> >> >> >> On Thu, Nov 3, 2016 at 5:05 PM, Dimitri Liakhovitski >> <dimitri.liakhovitski at gmail.com> wrote: >>> Hello! >>> >>> I have a matrix x and a vector y: >>> >>> x <- matrix(1:6, ncol = 2) >>> y <- c(2,3) >>> >>> I need to multiply the first column of x by 2 (y[1]) and the second >>> column of x by 3 (y[2]). >>> >>> Of course, I could do this - but it's column by column: >>> >>> x[,1] <- x[,1] * y[1] >>> x[,2] <- x[,2] * y[2] >>> x >>> >>> Or I could repeat each element of y and multiply two matrices - that's better: >>> >>> rep.row<-function(x,n){ >>> matrix(rep(x,each=n),nrow=n) >>> } >>> y <- rep.row(y, nrow(x)) >>> x * y >>> >>> However, maybe there is a more elegant r-like way of doing it? >>> Thank you! >>> >>> -- >>> Dimitri Liakhovitski >>> >> >> -- >> Sarah Goslee >> http://www.functionaldiversity.org >> >> ______________________________________________ >> 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.-- Dimitri Liakhovitski
Sara wins on memory use.
Rui wins on speed.
Bert wins on clarity.
library(microbenchmark)
N <- 1000
x <- matrix( runif( N*N ), ncol=N )
y <- seq.int( N )
microbenchmark( { t( y * t(x) ) }
, { x %*% diag( y ) }
, { sweep( x, 2, y, `*` ) }
)
Unit: milliseconds
expr min lq median uq max
neval
{ t(y * t(x)) } 6.659562 7.475414 7.871341 8.182623 47.01105
100
{ x %*% diag(y) } 9.859292 11.014021 11.281334 11.733825 48.79463
100
{ sweep(x, 2, y, `*`) } 16.535938 17.682175 18.283572 18.712342 55.47159
100
On Fri, 4 Nov 2016, Dimitri Liakhovitski wrote:
> Nice!
> Thanks a lot, everybody!
> Dimitri
>
> On Fri, Nov 4, 2016 at 10:35 AM, Bert Gunter <bgunter.4567 at
gmail.com> wrote:
>> My goodness!
>>
>>> x %*% diag(y)
>>
>> [,1] [,2]
>> [1,] 2 12
>> [2,] 4 15
>> [3,] 6 18
>>
>> will do.
>>
>> -- Bert
>>
>>
>>
>> Bert Gunter
>>
>> "The trouble with having an open mind is that people keep coming
along
>> and sticking things into it."
>> -- Opus (aka Berkeley Breathed in his "Bloom County" comic
strip )
>>
>>
>> On Thu, Nov 3, 2016 at 2:33 PM, Sarah Goslee <sarah.goslee at
gmail.com> wrote:
>>> Like this?
>>>
>>>> sweep(x, 2, y, "*")
>>> [,1] [,2]
>>> [1,] 2 12
>>> [2,] 4 15
>>> [3,] 6 18
>>>>
>>>
>>>
>>> On Thu, Nov 3, 2016 at 5:05 PM, Dimitri Liakhovitski
>>> <dimitri.liakhovitski at gmail.com> wrote:
>>>> Hello!
>>>>
>>>> I have a matrix x and a vector y:
>>>>
>>>> x <- matrix(1:6, ncol = 2)
>>>> y <- c(2,3)
>>>>
>>>> I need to multiply the first column of x by 2 (y[1]) and the
second
>>>> column of x by 3 (y[2]).
>>>>
>>>> Of course, I could do this - but it's column by column:
>>>>
>>>> x[,1] <- x[,1] * y[1]
>>>> x[,2] <- x[,2] * y[2]
>>>> x
>>>>
>>>> Or I could repeat each element of y and multiply two matrices -
that's better:
>>>>
>>>> rep.row<-function(x,n){
>>>> matrix(rep(x,each=n),nrow=n)
>>>> }
>>>> y <- rep.row(y, nrow(x))
>>>> x * y
>>>>
>>>> However, maybe there is a more elegant r-like way of doing it?
>>>> Thank you!
>>>>
>>>> --
>>>> Dimitri Liakhovitski
>>>>
>>>
>>> --
>>> Sarah Goslee
>>> http://www.functionaldiversity.org
>>>
>>> ______________________________________________
>>> 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.
>
>
>
> --
> Dimitri Liakhovitski
>
> ______________________________________________
> 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.
>
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