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Rau, Roland

2005-Jan-21 12:31 UTC

[R] Avoiding a Loop?

Dear R-Helpers,

I have a matrix where the first column is known. The second column is
the result of multiplying this first column with a constant "const".
The
third column is the result of multiplying the second column with
"const".....
So far, I did it like this (as a simplified example):

nr.of.columns <- 4

myconstant <- 27.5

mymatrix <- matrix(numeric(0), nrow=5, ncol=nr.of.columns)

mymatrix[,1] <- 1:5

for (i in 2:nr.of.columns) {
	mymatrix[,i] <- myconstant * mymatrix[,i-1]
}


Can anyone give me some advice whether it is possible to avoid this loop
(and if yes: how)?

Any suggestions are welcome!

Thanks,
Roland




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Liaw, Andy

2005-Jan-21 14:32 UTC

head link

[R] Avoiding a Loop?

If `v' the the vector in the first column and `k' is the constant, then
the
matrix has k^(j-1) * v in the jth column, right?
> k <- 27.5^seq(0, length=4)
> k
[1]     1.00    27.50   756.25 20796.88> outer(1:5, k, "*")     [,1]  [,2]    [,3]      [,4]
[1,]    1  27.5  756.25  20796.88
[2,]    2  55.0 1512.50  41593.75
[3,]    3  82.5 2268.75  62390.63
[4,]    4 110.0 3025.00  83187.50
[5,]    5 137.5 3781.25 103984.38

Andy
> From: Rau, Roland
> 
> Dear R-Helpers,
> 
> I have a matrix where the first column is known. The second column is
> the result of multiplying this first column with a constant 
> "const". The
> third column is the result of multiplying the second column with
> "const".....
> So far, I did it like this (as a simplified example):
> 
> nr.of.columns <- 4
> 
> myconstant <- 27.5
> 
> mymatrix <- matrix(numeric(0), nrow=5, ncol=nr.of.columns)
> 
> mymatrix[,1] <- 1:5
> 
> for (i in 2:nr.of.columns) {
> 	mymatrix[,i] <- myconstant * mymatrix[,i-1]
> }
> 
> 
> Can anyone give me some advice whether it is possible to 
> avoid this loop
> (and if yes: how)?
> 
> Any suggestions are welcome!
> 
> Thanks,
> Roland
> 
> 
> 
> 
> +++++
> This mail has been sent through the MPI for Demographic 
> Rese...{{dropped}}
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide! 
> http://www.R-project.org/posting-guide.html
> 
>

james.holtman@convergys.com

2005-Jan-21 14:56 UTC

head link

[R] Avoiding a Loop?

Does this do what you want?

nr.of.columns <- 4

myconstant <- 27.5

mymatrix <- matrix(myconstant, nrow=5, ncol=nr.of.columns)

mymatrix[,1] <- 1:5

t(apply(mymatrix, 1, function(x) cumprod(x)))


__________________________________________________________
James Holtman        "What is the problem you are trying to solve?"
Executive Technical Consultant  --  Office of Technology, Convergys
james.holtman at convergys.com
+1 (513) 723-2929



                      "Rau, Roland"
                      <Rau at demogr.mpg.de>          To:       <r-help
at stat.math.ethz.ch>
                      Sent by:                     cc:
                      r-help-bounces at stat.m        Subject:  [R] Avoiding a
Loop?
                      ath.ethz.ch


                      01/21/2005 07:31






Dear R-Helpers,

I have a matrix where the first column is known. The second column is
the result of multiplying this first column with a constant "const".
The
third column is the result of multiplying the second column with
"const".....
So far, I did it like this (as a simplified example):

nr.of.columns <- 4

myconstant <- 27.5

mymatrix <- matrix(numeric(0), nrow=5, ncol=nr.of.columns)

mymatrix[,1] <- 1:5

for (i in 2:nr.of.columns) {
             mymatrix[,i] <- myconstant * mymatrix[,i-1]
}


Can anyone give me some advice whether it is possible to avoid this loop
(and if yes: how)?

Any suggestions are welcome!

Thanks,
Roland




+++++
This mail has been sent through the MPI for Demographic Rese...{{dropped}}

______________________________________________
R-help at stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide!
http://www.R-project.org/posting-guide.html

Rau, Roland

2005-Jan-21 15:07 UTC

head link

[R] Avoiding a Loop?

Dear R-List,

thank you very much for the fast answers.
Andy Liaw and James Holtman both gave me some example code which does
exactly what I want.

I will now try to check which one is better suited for my actual matrix
(in terms of speed).

Thanks,
Roland


-----Original Message-----
From: james.holtman at convergys.com [mailto:james.holtman at convergys.com] 
Sent: Friday, January 21, 2005 3:57 PM
To: Rau, Roland
Cc: r-help at stat.math.ethz.ch; r-help-bounces at stat.math.ethz.ch
Subject: Re: [R] Avoiding a Loop?





Does this do what you want?

nr.of.columns <- 4

myconstant <- 27.5

mymatrix <- matrix(myconstant, nrow=5, ncol=nr.of.columns)

mymatrix[,1] <- 1:5

t(apply(mymatrix, 1, function(x) cumprod(x)))


__________________________________________________________
James Holtman        "What is the problem you are trying to solve?"
Executive Technical Consultant  --  Office of Technology, Convergys
james.holtman at convergys.com
+1 (513) 723-2929


 

                      "Rau, Roland"

                      <Rau at demogr.mpg.de>          To:
<r-help at stat.math.ethz.ch>

                      Sent by:                     cc:

                      r-help-bounces at stat.m        Subject:  [R]
Avoiding a Loop?

                      ath.ethz.ch

 

 

                      01/21/2005 07:31

 

 





Dear R-Helpers,

I have a matrix where the first column is known. The second column is
the result of multiplying this first column with a constant "const".
The
third column is the result of multiplying the second column with
"const".....
So far, I did it like this (as a simplified example):

nr.of.columns <- 4

myconstant <- 27.5

mymatrix <- matrix(numeric(0), nrow=5, ncol=nr.of.columns)

mymatrix[,1] <- 1:5

for (i in 2:nr.of.columns) {
             mymatrix[,i] <- myconstant * mymatrix[,i-1]
}


Can anyone give me some advice whether it is possible to avoid this loop
(and if yes: how)?

Any suggestions are welcome!

Thanks,
Roland




+++++
This mail has been sent through the MPI for Demographic
Rese...{{dropped}}

______________________________________________
R-help at stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide!
http://www.R-project.org/posting-guide.html





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Zoltan Barta

2005-Jan-21 15:27 UTC

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[R] Avoiding a Loop?

"Rau, Roland" <Rau at demogr.mpg.de> writes:
> Dear R-Helpers,
>
> I have a matrix where the first column is known. The second column is
> the result of multiplying this first column with a constant
"const". The
> third column is the result of multiplying the second column with
> "const".....
> So far, I did it like this (as a simplified example):
>
> nr.of.columns <- 4
>
> myconstant <- 27.5
>
> mymatrix <- matrix(numeric(0), nrow=5, ncol=nr.of.columns)
>
> mymatrix[,1] <- 1:5
>
> for (i in 2:nr.of.columns) {
> 	mymatrix[,i] <- myconstant * mymatrix[,i-1]
> }
>
>
> Can anyone give me some advice whether it is possible to avoid this loop
> (and if yes: how)?
>
How about:
> myconstant <- 27.5
> a <- 1:5
> myconstant <- myconstant^((1:nr.of.columns)-1)
> myconstant
[1]     1.00    27.50   756.25 20796.88> mymatrix <- outer(a,myconstant)
> mymatrix     [,1]  [,2]    [,3]      [,4]
[1,]    1  27.5  756.25  20796.88
[2,]    2  55.0 1512.50  41593.75
[3,]    3  82.5 2268.75  62390.62
[4,]    4 110.0 3025.00  83187.50
[5,]    5 137.5 3781.25 103984.38> 
HTH

Zoltan
> Any suggestions are welcome!
>
> Thanks,
> Roland
>
>
>
>
> +++++
> This mail has been sent through the MPI for Demographic Rese...{{dropped}}
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide!
http://www.R-project.org/posting-guide.html
-- 


Z. Barta 
Dept. of Evol. Zool., Univ. of Debrecen, Debrecen, H-4010, Hungary
Phone: 36 52 316 666 ext. 2334, Fax: 36 52 533 677
E-mail: zbarta at delfin.unideb.hu, http://puma.unideb.hu/~zbarta/

Uwe Ligges

2005-Jan-21 15:30 UTC

head link

[R] Avoiding a Loop?

Rau, Roland wrote:
> Dear R-Helpers,
> 
> I have a matrix where the first column is known. The second column is
> the result of multiplying this first column with a constant
"const". The
> third column is the result of multiplying the second column with
> "const".....
> So far, I did it like this (as a simplified example):
> 
> nr.of.columns <- 4
> 
> myconstant <- 27.5
> 
> mymatrix <- matrix(numeric(0), nrow=5, ncol=nr.of.columns)
> 
> mymatrix[,1] <- 1:5
> 
> for (i in 2:nr.of.columns) {
> 	mymatrix[,i] <- myconstant * mymatrix[,i-1]
> }
   nr.of.columns <- 4
   myconstant <- 27.5
   mycolumn <- 1:5
   outer(mycolumn, myconstant^(0:(nr.of.columns-1)))

Uwe Ligges


> 
> Can anyone give me some advice whether it is possible to avoid this loop
> (and if yes: how)?
> 
> Any suggestions are welcome!
> 
> Thanks,
> Roland
> 
> 
> 
> 
> +++++
> This mail has been sent through the MPI for Demographic Rese...{{dropped}}
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide!
http://www.R-project.org/posting-guide.html

Berton Gunter

2005-Jan-21 17:47 UTC

head link

[R] Avoiding a Loop?

Roland:

Andy Liaw and others have already given perfectly good answers to this (but
note: Using apply() type functions does **not** avoid loops; apply's **are**
loops). However, mostly as an illustration to reinforce Uwe Ligges's
comments (in the "dim vs length" thread) about the usefulness of
sometimes
treating arrays as vectors, I offer the following:

nc<-ncol(yourmatrix)
matrix(yourmatrix[,1]*rep(k^seq(0,length=nc),e=nrow(yourmatrix)),ncol=nc)

Alteratively, one could use matrix multiplication:

yourmatrix[,1]%*%matrix(k^seq(0,length=nc),nrow=1)

Both of these will be very fast (although unlikely to make a noticeable
difference without a lot of rows or columns) and I think use less memory
than outer() (again, unlikely to make a noticeable difference).


-- Bert Gunter
Genentech Non-Clinical Statistics
South San Francisco, CA
 
> -----Original Message-----
> From: r-help-bounces at stat.math.ethz.ch 
> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Rau, Roland
> Sent: Friday, January 21, 2005 4:32 AM
> To: r-help at stat.math.ethz.ch
> Subject: [R] Avoiding a Loop?
> 
> Dear R-Helpers,
> 
> I have a matrix where the first column is known. The second column is
> the result of multiplying this first column with a constant 
> "const". The
> third column is the result of multiplying the second column with
> "const".....
> So far, I did it like this (as a simplified example):
> 
> nr.of.columns <- 4
> 
> myconstant <- 27.5
> 
> mymatrix <- matrix(numeric(0), nrow=5, ncol=nr.of.columns)
> 
> mymatrix[,1] <- 1:5
> 
> for (i in 2:nr.of.columns) {
> 	mymatrix[,i] <- myconstant * mymatrix[,i-1]
> }
> 
> 
> Can anyone give me some advice whether it is possible to 
> avoid this loop
> (and if yes: how)?
> 
> Any suggestions are welcome!
> 
> Thanks,
> Roland
> 
> 
> 
> 
> +++++
> This mail has been sent through the MPI for Demographic 
> Rese...{{dropped}}
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide! 
> http://www.R-project.org/posting-guide.html
>

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