[R] Product of certain rows in a matrix
arun
smartpink111 at yahoo.com
Mon Sep 2 18:07:00 CEST 2013
Hi,
No problem.
n<- 4
t(sapply(split(as.data.frame(Anew),as.numeric(gl(nrow(Anew),n,nrow(Anew)))),function(x) apply(x,2,prod)))
# V1 V2 V3
#1 252 640 1134
#2 18 30 20
This could be a bit slow if you have big dataset.
A.K.
________________________________
From: Edouard Hardy <hardy.edouard at gmail.com>
To: arun <smartpink111 at yahoo.com>
Cc: R help <r-help at r-project.org>
Sent: Monday, September 2, 2013 11:58 AM
Subject: Re: [R] Product of certain rows in a matrix
Thank you A.K.
And do you have a solution without installing any package ?
Thank you in advance.
E.H.
Edouard Hardy
On Mon, Sep 2, 2013 at 5:56 PM, arun <smartpink111 at yahoo.com> wrote:
>
>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.
>>
>
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