[R] sum of unknown number of matrices

2008-06-04 Thread Shubha Vishwanath Karanth 
Hi R,

 

I have a list of matrices. I need to get the sum of all the matrices in
the list.

 

Example:

a=b=c=d=matrix(1:4,2,2)

l=list(a,b,c,d)

 

 

I need:

 a+b+c+d

 [,1] [,2]

[1,]4   12

[2,]8   16

 

Something like do.call(+,l) is not working...why is this?

 

 

I may not be knowing the number of matrices in the list...

 

Thanks, Shubha

 

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Re: [R] sum of unknown number of matrices

2008-06-04 Thread Dimitris Rizopoulos 

try a simple for loop, it will be fast enough in this case, e.g.,

matSums - function (lis) {
   out - array(data = 0, dim = dim(lis[[1]]))
   for (i in seq(along = lis))
   out - out + lis[[i]]
   out
}

a - b - c - d - matrix(1:4, 2, 2)
l - list(a, b ,c, d)

matSums(l)


I hope it helps.

Best,
Dimitris


Dimitris Rizopoulos
Biostatistical Centre
School of Public Health
Catholic University of Leuven

Address: Kapucijnenvoer 35, Leuven, Belgium
Tel: +32/(0)16/336899
Fax: +32/(0)16/337015
Web: http://med.kuleuven.be/biostat/
http://www.student.kuleuven.be/~m0390867/dimitris.htm


- Original Message - 
From: Shubha Vishwanath Karanth [EMAIL PROTECTED]

To: [EMAIL PROTECTED]
Sent: Wednesday, June 04, 2008 4:53 PM
Subject: [R] sum of unknown number of matrices



Hi R,



I have a list of matrices. I need to get the sum of all the matrices 
in

the list.



Example:

a=b=c=d=matrix(1:4,2,2)

l=list(a,b,c,d)





I need:


a+b+c+d


[,1] [,2]

[1,]4   12

[2,]8   16



Something like do.call(+,l) is not working...why is this?





I may not be knowing the number of matrices in the list...



Thanks, Shubha



This e-mail may contain confidential and/or privileged 
i...{{dropped:13}}


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Disclaimer: http://www.kuleuven.be/cwis/email_disclaimer.htm

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Re: [R] sum of unknown number of matrices

2008-06-04 Thread Barry Rowlingson 

Shubha Vishwanath Karanth wrote:


I need:


a+b+c+d


 [,1] [,2]

[1,]4   12

[2,]8   16

 


Something like do.call(+,l) is not working...why is this?


Because do.call constructs a function call with the elements of l as 
arguments, so you end up with:


+(1:4, 1:4, 1:4, 1:4)

 but + only takes two arguments.

Use 'Reduce':

  Reduce(+,l)
  [,1] [,2]
 [1,]4   12
 [2,]8   16

 Barry

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Re: [R] sum of unknown number of matrices

2008-06-04 Thread John Fox 
Dear Shubha,

This problem was coincidentally used as an illustration in the Help Desk
column in the current R News.

Actually, the brute-force method of using a loop to accumulate the sum works
quite well; a more elegant alternative, recently brought to my attention by
Kurt Hornik, uses the Reduce() function.

Here's an example:

 matrices - vector(mode=list, length=1)
 for (i in 1:1)
+   matrices[[i]] - matrix(rnorm(1), 100, 100)
 
 system.time({
+   S - matrix(0, 100, 100)
+   for (i in 1:1) S - S + matrices[[i]]
+   })
   user  system elapsed 
   0.590.000.59 
   
 system.time(S1 - Reduce(+, matrices))
   user  system elapsed 
   0.600.000.59 
 
 range(S1 - S)
[1] 0 0

I hope this helps,
 John

--
John Fox, Professor
Department of Sociology
McMaster University
Hamilton, Ontario, Canada
web: socserv.mcmaster.ca/jfox

 -Original Message-
 From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]
On
 Behalf Of Shubha Vishwanath Karanth
 Sent: June-04-08 10:54 AM
 To: [EMAIL PROTECTED]
 Subject: [R] sum of unknown number of matrices
 
 Hi R,
 
 
 
 I have a list of matrices. I need to get the sum of all the matrices in
 the list.
 
 
 
 Example:
 
 a=b=c=d=matrix(1:4,2,2)
 
 l=list(a,b,c,d)
 
 
 
 
 
 I need:
 
  a+b+c+d
 
  [,1] [,2]
 
 [1,]4   12
 
 [2,]8   16
 
 
 
 Something like do.call(+,l) is not working...why is this?
 
 
 
 
 
 I may not be knowing the number of matrices in the list...
 
 
 
 Thanks, Shubha
 
 
 
 This e-mail may contain confidential and/or privileged i...{{dropped:13}}
 
 __
 R-help@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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Re: [R] sum of unknown number of matrices

2008-06-04 Thread Shubha Vishwanath Karanth 
Thanks all...Reduce() is the new function I learnt today... Thanks...

BR, Shubha
Shubha Karanth | Amba Research
Ph +91 80 3980 8031 | Mob +91 94 4886 4510 
Bangalore * Colombo * London * New York * San José * Singapore * 
www.ambaresearch.com
-Original Message-
From: Barry Rowlingson [mailto:[EMAIL PROTECTED] 
Sent: Wednesday, June 04, 2008 8:49 PM
To: Shubha Vishwanath Karanth
Cc: [EMAIL PROTECTED]
Subject: Re: [R] sum of unknown number of matrices

Shubha Vishwanath Karanth wrote:

 I need:
 
 a+b+c+d
 
  [,1] [,2]
 
 [1,]4   12
 
 [2,]8   16
 
  
 
 Something like do.call(+,l) is not working...why is this?

Because do.call constructs a function call with the elements of l as 
arguments, so you end up with:

+(1:4, 1:4, 1:4, 1:4)

  but + only takes two arguments.

Use 'Reduce':

   Reduce(+,l)
   [,1] [,2]
  [1,]4   12
  [2,]8   16

  Barry


This e-mail may contain confidential and/or privileged i...{{dropped:10}}

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Re: [R] sum of unknown number of matrices

2008-06-04 Thread Berwin A Turlach 
G'day Shubha,

On Wed, 4 Jun 2008 20:23:35 +0530
Shubha Vishwanath Karanth [EMAIL PROTECTED] wrote:

 Something like do.call(+,l) is not working...why is this?

Well, as the error message says, + is either a unary or a binary
operator, i.e. it takes either one or two arguments, but not more.

 I may not be knowing the number of matrices in the list...

This is perhaps a bit complicated but it works:

R a=b=c=d=matrix(1:4,2,2)
R l=list(a,b,c,d)
R library(abind)  ## may have to install this package first
R apply(do.call(abind, list(l, along=3)), 1:2, sum)
 [,1] [,2]
[1,]4   12
[2,]8   16

HTH.

Cheers,

Berwin

=== Full address =
Berwin A TurlachTel.: +65 6515 4416 (secr)
Dept of Statistics and Applied Probability+65 6515 6650 (self)
Faculty of Science  FAX : +65 6872 3919   
National University of Singapore
6 Science Drive 2, Blk S16, Level 7  e-mail: [EMAIL PROTECTED]
Singapore 117546http://www.stat.nus.edu.sg/~statba

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