# [R] Working with Matrix

Christofer Bogaso bogaso.christofer at gmail.com
Fri Jan 4 19:46:10 CET 2013

```Thanks all for your help. However I was looking for following type of operation:

Mat1 <- Mat2 <- matrix(1:20, 4, 5); Mat2[1,5] <- 200
Mat = rbind(Mat1, Mat2)
apply(Mat, 2, function(x) return(all(x[1:4] == x[5:8])))

However I believe there must be some smarter method using
***mapply()*** or something like that. To me above operation looks
very trivial! Also underlying function may be more complected

Is it real trivial or some better method is available?

Thanks and regards,

On Fri, Jan 4, 2013 at 9:24 PM, Suzen, Mehmet <msuzen at gmail.com> wrote:
> Hello Rui/Jorge,
>
> This is shorter, and probably needs less memory for large matrices as
> you create
> an other copy by defining nas:
>
> matrixOp <- function(m1, m2, op=`+`) {
>  rows <- min(nrow(m1), nrow(m2))
>  cols <- ncol(m1)
>  op(m1[1:rows, 1:cols], m2[1:rows, 1:cols])
> }
>
> Best,
>
> mem
>
> On 4 January 2013 14:08, Rui Barradas <ruipbarradas at sapo.pt> wrote:
>> Hello,
>>
>> Using part of your code, it's possible to do without Reduce, have foo (fun,
>> below) do the job.
>>
>> fun <- function(x, y, FUN = `+`){
>>     if(nrow(x) < nrow(y)){
>>         nas <- matrix(NA, ncol = ncol(x), nrow = nrow(y) - nrow(x))
>>         x <- rbind(x, nas)
>>     }else{
>>         nas <- matrix(NA, ncol = ncol(y), nrow = nrow(x) - nrow(y))
>>         y <- rbind(y, nas)
>>     }
>>     FUN(x, y)
>> }
>>
>> fun(Mat1, Mat2)
>> fun(Mat1, Mat2, `*`)  # Note the back quotes
>>
>>
>> Hope this helps,
>>
>> Em 04-01-2013 12:06, Jorge I Velez escreveu:
>>
>>> Dear Christofer,
>>>
>>> You can try the following:
>>>
>>> # proccess the matrices
>>> foo <- function(m1, m2){
>>>   if(ncol(m1) != ncol(m2)) stop('number of columns should be equal')
>>>   if(nrow(m1) < nrow(m2)){
>>> nas <- matrix(NA, ncol = ncol(m1), nrow = nrow(m2) - nrow(m1))
>>>   m1 <- rbind(m1, nas)
>>> }
>>> else{
>>>   nas <- matrix(NA, ncol = ncol(m1), nrow = nrow(m1) - nrow(m2))
>>> m2 <- rbind(m2, nas)
>>>   }
>>>   list(m1, m2)
>>> }
>>>
>>> # process
>>> r <- foo(Mat1, Mat2)
>>>
>>> # basic operations
>>> Reduce("+", r)
>>> Reduce("*", r)
>>> Reduce("/", r)
>>> Reduce("-", r)
>>>
>>> HTH,
>>> Jorge.-
>>>
>>>
>>> On Fri, Jan 4, 2013 at 10:47 PM, Christofer Bogaso <> wrote:
>>>
>>>> Hello again,
>>>>
>>>> Let say I have 2 matrices which equal number of columns but different
>>>> number of rows like:
>>>>
>>>> Mat1 <- matrix(1:20, 4, 5)
>>>> Mat2 <- matrix(1:25, 5, 5)
>>>>
>>>> Now for each column 1-to-5 I need to fetch the corresponding columns
>>>> of these 2 matrices and add the corresponding elements (ignoring NA
>>>> values if any). Therefore for the 1st column I need to do:
>>>>
>>>> (1+1), (2+2),...,(4+4), (NA+5)
>>>>
>>>> and so on
>>>>
>>>> And the resulting numbers will be stored in some other matrix
>>>>
>>>> Also note that, here I gave the example of addition, however, this can
>>>> be any user defined function.
>>>>
>>>> Is there any R way to do that, without using any for-loop?
>>>>
>>>> Thanks and regards,
>>>>
>>>> ______________________________________________
>>>> 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.
>>>>
>>>         [[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.
>>
>>
>> ______________________________________________
>> 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.
>
> ______________________________________________
> 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.

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