Hello everybody.
Thank you again to Bert and Arun for their help on my previous question.
I know have the following problem:
I have a matrix :
A =
1 2 3
4 5 6
7 8 9
9 8 7
4 5 6
3 2 1
And I would like to have :
B =
1*4*7 2*5*8 3*6*9
4*7*9 5*8*8 6*9*7
7*9*4 8*8*5 9*7*6
9*4*3
Hello, Edouard,
taking logs of A's elements (so that * turns into +, so to say), using a
left-multiplication with a certain band matrix of the package Matrix, and
exponentiating the result again could provide a solution (see below).
I know have the following problem:
I have a matrix :
A =
1
Thank you very much for your answer.
Unfortunately, I cannot use any package...
Do you have a solution ?
Thank you in advance
Edouard Hardy
On Tue, Sep 3, 2013 at 11:49 AM, Gerrit Eichner
gerrit.eich...@math.uni-giessen.de wrote:
Hello, Edouard,
taking logs of A's elements (so that *
Thank you very much for your answer. Unfortunately, I cannot use any
package...
Er, ... this is quite unusual! (Is this is homework?)
Do you have a solution ?
Well, take a look at the resulting bandmatrix leftmatrix. Yould can
certainly build it yourself by hand somehow. I used the Matrix
Subject: [R] Product of certain rows in a matrix without loop
Hello everybody.
Thank you again to Bert and Arun for their help on my previous
question.
I know have the following problem:
I have a matrix :
A =
1 2 3
4 5 6
7 8 9
9 8 7
4 5 6
3 2 1
And I would like to have
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
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,] 18 104
[,1] [,2] [,3]
[1,]4 10 18
[2,] 63 64 63
[3,] 18 104
[,1]
4 10 18
2 63 64 63
3 18 10 4
4 1 3 5
A.K.
From: Bert Gunter gunter.ber...@gene.com
To: arun smartpink...@yahoo.com
Cc: R help r-help@r-project.org
Sent: Monday, September 2, 2013 10:55 AM
Subject: Re: [R] Product of certain rows
: 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
-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
hardy.edou...@gmail.com
To: arun smartpink...@yahoo.com
Cc: R help r-help@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
...@yahoo.com
To: Edouard Hardy hardy.edou...@gmail.com
Cc: R help r-help@r-project.org; Bert Gunter gunter.ber...@gene.com
Sent: Monday, September 2, 2013 12:07 PM
Subject: Re: [R] Product of certain rows in a matrix
Hi,
No problem.
n- 4
t(sapply(split(as.data.frame(Anew),as.numeric(gl(nrow(Anew
gunter.ber...@gene.com
Sent: Monday, September 2, 2013 12:07 PM
Subject: Re: [R] Product of certain rows in a matrix
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
...@gmail.com
To: arun smartpink...@yahoo.com
Sent: Monday, September 2, 2013 2:32 PM
Subject: Re: [R] Product of certain rows in a matrix
Yes, n is 250 or more...
Edouard Hardy
On Mon, Sep 2, 2013 at 8:31 PM, arun smartpink...@yahoo.com wrote:
Also, BTW, are you looking for n100
:31 PM
Subject: Re: [R] Product of certain rows in a matrix
There was a slight mistake in the end:
I repeated vec1. But, it doesn't matter as the warning messages are the same.
j40- n*seq_len(nrow(mat1)/n)
vec1- rep(j40,n)
res- eval(parse(text=
paste(paste0(mat1,[,paste0(vec1,-,seq(n)-1
-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
: Edouard Hardy hardy.edou...@gmail.com
To: arun smartpink...@yahoo.com
Cc: Bert Gunter gunter.ber...@gene.com; R help r-help@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
Gents:
The eval(parse(...)) construction should almost always be avoided: it is
basically a misuse of R. There are exceptions, I suppose, but this does not
appear to be one of them.
Note that the use of numeric indexing does appear to be slightly faster
than logical indexing here, although I
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