[R] Product of certain rows in a matrix

[arun]

HI,
In my first solutions:
 n<-3
 t(sapply(split(as.data.frame(Anew),as.numeric(gl(nrow(Anew),n,nrow(Anew)))),colProds))
#  [,1] [,2] [,3]
#1   28   80  162
#2  162   80   28
#3    1    3    5
 n<-4
 t(sapply(split(as.data.frame(Anew),as.numeric(gl(nrow(Anew),n,nrow(Anew)))),colProds))
#  [,1] [,2] [,3]
#1  252  640 1134
#2   18   30   20

A.K.
________________________________
From: Edouard Hardy <hardy.edouard at gmail.com>
To: arun <smartpink111 at yahoo.com> 
Cc: Bert Gunter <gunter.berton at gene.com>; R help <r-help at r-project.org> 
Sent: Monday, September 2, 2013 11:46 AM
Subject: Re: [R] Product of certain rows in a matrix



Thank you all for your responses.
The real problem is that all your answer work for products 2 by 2.
I now have to do the product n by n row.
Do you have a solution ?
Thank you in advance,
E.H. 



Edouard Hardy



On Mon, Sep 2, 2013 at 5:43 PM, arun <smartpink111 at yahoo.com> wrote:

I guess in such situations,
>
>
>fun1<- function(mat){
> if(nrow(mat)%%2==0){
> j<- 2*seq_len(nrow(mat)/2)
> b<- mat[j,]* mat[j-1,]
> }
> else {mat1<- mat[-nrow(mat),]
> j<- 2*seq_len(nrow(mat1)/2)
> b<- rbind(mat1[j,]*mat1[j-1,],mat[nrow(mat),])
>  }
>b
>}
>fun1(A)
>#     [,1] [,2] [,3]
>
>#[1,]    4   10   18
>#[2,]   63   64   63
>#[3,]   18   10    4
> fun1(Anew)
>#     [,1] [,2] [,3]
>
>#[1,]    4   10   18
>#[2,]   63   64   63
>#[3,]   18   10    4
>#[4,]    1    3    5
>
>
>A.K.
>
>
>
>
>----- Original Message -----
>From: arun <smartpink111 at yahoo.com>
>To: Bert Gunter <gunter.berton at gene.com>
>Cc: R help <r-help at r-project.org>
>
>Sent: Monday, September 2, 2013 11:26 AM
>Subject: Re: [R] Product of certain rows in a matrix
>
>Hi Bert,
>Thanks.  It is a better solution.
>
>If nrow() is not even.
>
>Anew<- rbind(A,c(1,3,5))
>j<-seq_len(nrow(Anew)/2)###
> Anew[j,]*Anew[j-1,]
>#Error in Anew[j, ] * Anew[j - 1, ] : non-conformable arrays
>
>t(sapply(split(as.data.frame(Anew),as.numeric(gl(nrow(Anew),2,7))),colProds))
>  [,1] [,2] [,3]
>1    4   10   18
>2   63   64   63
>3   18   10    4
>4    1    3    5
>
>A.K.
>
>
>
>
>
>
>________________________________
>From: Bert Gunter <gunter.berton at gene.com>
>To: arun <smartpink111 at yahoo.com>
>Cc: R help <r-help at r-project.org>
>Sent: Monday, September 2, 2013 10:55 AM
>Subject: Re: [R] Product of certain rows in a matrix
>
>
>
>These elaborate manipulations are unnecessary and inefficient. Use indexing instead:
>
>j <- 2*seq_len(nrow(A)/2)
>b <- A[j,]*A[j-1,]
>b
>[,1] [,2] [,3]
>[1,]    4   10   18
>[2,]   63   64   63
>[3,]   18   10    4
>
>[,1] [,2] [,3]
>[1,]    4   10   18
>[2,]   63   64   63
>[3,]   18   10    4
>[,1] [,2] [,3]
>[1,]    4   10   18
>[2,]   63   64   63
>[3,]   18   10    4[,1] [,2] [,3]
>[1,]    4   10   18
>[2,]   63   64   63
>[3,]   18   10    4
>[,1] [,2] [,3]
>[1,]    4   10   18
>[2,]   63   64   63
>[3,]   18   10    4
>
>
>
>
>
>On Mon, Sep 2, 2013 at 7:25 AM, arun <smartpink111 at yahoo.com> wrote:
>
>Hi,
>>You could try:
>>
>>A<- matrix(unlist(read.table(text="
>>1 2 3
>>4 5 6
>>7 8 9
>>9 8 7
>>6 5 4
>>3 2 1
>>",sep="",header=FALSE)),ncol=3,byrow=FALSE,dimnames=NULL)
>>
>>library(matrixStats)
>> res1<-t(sapply(split(as.data.frame(A),as.numeric(gl(nrow(A),2,6))),colProds))
>> res1
>>#  [,1] [,2] [,3]
>>#1    4   10   18
>>#2   63   64   63
>>#3   18   10    4
>>
>>
>> res2<-t(sapply(split(as.data.frame(A),((seq_len(nrow(A))-1)%/%2)+1),colProds))
>> identical(res1,res2)
>>#[1] TRUE
>>
>>#or
>> t(sapply(split(as.data.frame(A),as.numeric(gl(nrow(A),2,6))),function(x) apply(x,2,prod)))
>>
>>#or
>>library(plyr)
>> as.matrix(ddply(as.data.frame(A),.(as.numeric(gl(nrow(A),2,6))),colProds)[,-1])
>>#     V1 V2 V3
>>#[1,]  4 10 18
>>#[2,] 63 64 63
>>#[3,] 18 10  4
>>
>>#or
>>do.call(rbind,tapply(seq_len(nrow(A)),list(as.numeric(gl(nrow(A),2,6))),FUN=function(x) colProds(A[x,])))
>>#or
>>A1<- data.frame(A,ID=as.numeric(gl(nrow(At),2,6)))
>> aggregate(A1[,-4],list(A1[,4]),colProds)[,-1]
>>#  X1 X2 X3
>>#1  4 10 18
>>#2 63 64 63
>>#3 18 10  4
>>
>>#or
>>library(data.table)
>>At<- data.table(A1,key='ID')
>>subset(At[,lapply(.SD,colProds),by=ID],select=-1)
>>#   X1 X2 X3
>>#1:  4 10 18
>>#2: 63 64 63
>>#3: 18 10  4
>>
>>A.K.
>>
>>
>>
>>
>>Hello,
>>
>>I have this matrix :
>>A =
>>1 2 3
>>4 5 6
>>7 8 9
>>9 8 7
>>6 5 4
>>3 2 1
>>
>>I would like to have this matrix (product of rows 2 by 2) :
>>A =
>>4 10 18
>>63 64 63
>>18 10 4
>>
>>Is it possible to do that without a loop ?
>>
>>Thank you in advance !
>>
>>______________________________________________
>>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.
>>
>
>
>--
>
>
>Bert Gunter
>Genentech Nonclinical Biostatistics
>
>Internal Contact Info:
>Phone: 467-7374
>Website:
>
>http://pharmadevelopment.roche.com/index/pdb/pdb-functional-groups/pdb-biostatistics/pdb-ncb-home.htm
>
>______________________________________________
>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.
>