Here's one way:
y/outer(rep(1, nrow(y)), x)
[,1] [,2] [,3] [,4] [,5]
[1,] 1 3.5 4.333333 4.75 5.0
[2,] 2 4.0 4.666667 5.00 5.2
[3,] 3 4.5 5.000000 5.25 5.4
[4,] 4 5.0 5.333333 5.50 5.6
[5,] 5 5.5 5.666667 5.75 5.8
[6,] 6 6.0 6.000000 6.00 6.0
Run the outer command by itself to see what it does.
HTH,
Dennis
On Thu, Jan 27, 2011 at 7:18 AM, adam_pgsql <adam_pg...@witneyweb.org>wrote:
>
> Hi,
>
> I'd like to divide each element of a matrix by a specific value per column.
> These specific values are stored in a list. For example:
>
> > x <- c(1,2,3,4,5)
> > y <- matrix(c(1:30), nrow = 6)
>
> Now I want to divide each element in y[,1] by x[1], y[,2] by x[2] etc. I
> have tried this
>
> > my_function <- function(data, ind) data/ind
> > apply(y, 2, my_function, x)
> [,1] [,2] [,3] [,4] [,5]
> [1,] 1 7.0 13.0 19.0 25.0
> [2,] 1 4.0 7.0 10.0 13.0
> [3,] 1 3.0 5.0 7.0 9.0
> [4,] 1 2.5 4.0 5.5 7.0
> [5,] 1 2.2 3.4 4.6 5.8
> [6,] 6 12.0 18.0 24.0 30.0
> Warning messages:
> 1: In data/ind :
> longer object length is not a multiple of shorter object length
> 2: In data/ind :
> longer object length is not a multiple of shorter object length
> 3: In data/ind :
> longer object length is not a multiple of shorter object length
> 4: In data/ind :
> longer object length is not a multiple of shorter object length
> 5: In data/ind :
> longer object length is not a multiple of shorter object length
>
> but as you can see it is applying them by row rather than column. Any ideas
> how to do this? Is there a variable within 'apply' that can be used to
> determine which column of y is being processed?
>
> thanks for any help
>
> adam
>
> > sessionInfo()
> R version 2.11.1 (2010-05-31)
> x86_64-apple-darwin9.8.0
>
> locale:
> [1] en_GB.UTF-8/en_GB.UTF-8/C/C/en_GB.UTF-8/en_GB.UTF-8
>
> attached base packages:
> [1] stats graphics grDevices utils datasets methods base
>
> ______________________________________________
> 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.
>
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